Method for producing solid electrolyte, and electrolyte precursor

ABSTRACT

A solid electrolyte contains a thio-LISICON Region II-type crystal structure, where the solid electrolyte does not contain P2S64− structure. A solid electrolyte, where:(1) a signal of a thio-LISICON Region II-type crystal structure is observed in the solid 31P-NMR spectrometry, and(2) a signal of a P2S64− structure is not observed in the solid 31P-NMR spectrometry.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/254,543, filed on Dec. 21,202, which is a national stage patentapplication of international patent application PCT/JP2019104-5852,filed on Nov. 22, 2019, the text of which is incorporated by reference,and claims foreign priority to Japanese Patent Application No.2019-148210, filed on Aug. 9, 2019, and Japanese Patent Application No.2018-219130, filed on Nov. 22, 2018, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

The present. invention relates to a method for producing a solidelectrolyte and an electrolyte precursor,

BACKGROUND ART

With rapid spread of information-related instruments, communicationinstruments, and so on, such as personal computers, video cameras, andmobile phones, in recent years, development of batteries that areutilized as a power source therefor is considered to be important.Heretofore, in batteries to be used for such an application, anelectrolytic solution containing a flammable organic solvent has beenused. However, development of batteries having a solid electrolyte layerin place of an electrolytic solution is being made in view of the factthat by making the battery solid, simplification of a safety unit may berealized without using a flammable organic solvent within the battery,and the battery is excellent in manufacturing costs and productivity.

A production method of a solid electrolyte to be used for a solidelectrolyte layer is roughly classified into a solid-phase method and aliquid-phase method. Furthermore, as for the liquid-phase method, thereare a homogeneous method in which a solid electrolyte material iscompletely dissolved in a solvent; and a heterogeneous method in which asolid electrolyte material is not completely dissolved in a solvent butundergoes through a suspension of solid-liquid coexistence. For example,as the solid-phase method, a method in which raw materials, such asliquid sulfide and diphosphorus pentasulfide are subjected to mechanicalmilling treatment using an apparatus, such as a ball mill and a beadmill and optionally subjected to heat treatment, thereby producing anamorphous or crystalline solid electrolyte is known (see, for example,PTL 1). In accordance with this method, the solid electrolyte isobtained by applying a mechanical stress to the raw materials, such aslithium sulfide, to promote the reaction of the solids with each other.

On the other hand, as for the homogenous method regarding theliquid-phase method, a method in which a solid electrolyte is dissolvedin a solvent and redeposited is known (see, for example, PTL 2). Inaddition, as for the heterogeneous method, a method in which solidelectrolyte raw materials, such as lithium sulfide, are allowed to reactin a solvent containing a polar aprotic solvent. is known (see, forexample, PTLs 3 and 4 and NFL 1). For example, PTL 4 discloses that aproduction method of a solid electrolyte having an Li₄PS₄I structureincludes a step in which dimethoxyethane (DME) is used and bound withthe Li₃PS₄ structure, to obtain Li₄PS₄·DME. The obtained solidelectrolyte has an ionic conductivity of 5.5×10⁻⁵ Skin (3.9×10⁻⁴ S/cm inthe calcium-doped product). Toward practical use of an all-solid-statebattery, the liquid-phase method is recently watched as a method inwhich it can be synthesized simply and in a large amount in addition toversatility and applicability.

CITATION LIST Patent Literature

PTL 1: WO 2017/159667 A

PTL 2: JP 2014-191899 A

PTL 3: WO 20141192309 A

PTL 4: WO 2018/054709 A

Non-Patent Literature

NPL 1: CHEMISTRY OF MATERIALS, 2017, No. 29, pp. 1830-1835

SUMMARY OF INVENTION Technical Problem

However, as for the conventional solid-phase method accompanied withmechanical milling treatment or the like, the solid-phase reaction isthe center, and the solid electrolyte is readily obtained in a highpurity, and thus, a high ionic conductivity can be realized. On theother hand, as for the liquid-phase method, for the reasons that thesolid electrolyte is dissolved, and thus, decomposition, breakage, orthe like of a part of the solid electrolyte components is generatedduring deposition, it was difficult to realize a high ionic conductivityas compared with the solid-phase synthesis method.

For example, according to the homogenous method, the raw materials orthe solid electrolyte is once completely dissolved, and thus, thecomponents can be homogenously dispersed in the liquid. But, in thesubsequent deposition step, the deposition proceeds according to aninherent solubility of each of the components, and thus, it is extremelydifficult to perform the deposition while keeping the dispersed state ofthe components. As a result, each of the components is separated anddeposited. In addition, according to the homogenous method, an affinitybetween the solvent and lithium becomes excessively strong, andtherefore, even by ding after deposition, the solvent hardly comes out.For these matters, the homogenous method involves such a problem thatthe ionic conductivity of the solid electrolyte is largely lowered.

In addition, even in the heterogeneous method of solid-liquidcoexistence, a part of the solid electrolyte is dissolved, and thus,separation takes place owing to elution of the specified component, sothat it is difficult to obtain a desired solid electrolyte.

Furthermore, as for a sulfide-based solid electrolyte, for the reasonthat hydrolysis reaction proceeds owing to contact with water in air,such as moisture, or other reason, there is a case where hydrogensulfide is generated. In consequence, it is an ideal that a productionprocess of a solid electrolyte or a battery is performed in a low dewpoint environment with less moisture; however, it is difficulteconomically and physically to perform all of steps at a high dew point,and actually, it is required to handle the solid electrolyte at a highdew point (for example, (dew point) −60° C. to −20° C.) in a dry roomlevel. However, a sulfide-based solid electrolyte which is able to behandled at such a high dew point and also has practical performance hasnot been found out yet.

In view of the aforementioned circumstances, the present invention hasbeen made, and an object thereof is to provide a production method inwhich adopting a liquid-phase method, a solid electrolyte having a highionic conductivity, in which the generation of hydrogen sulfide issuppressed in a predetermined high dew point environment, is obtained;and an electrolyte precursor.

Solution to Problem

In order to solve the aforementioned problem, the present inventor madeextensive and intensive investigations. As a result, it has been foundthat the foregoing problem can be solved by the following inventions.

1. A production method of a solid electrolyte, including mixing a rawmaterial inclusion containing a lithium element, a sulfur element, aphosphorus element, and a halogen element with a complexing agentcontaining a compound having at least two tertiary amino groups in themolecule.

An electrolyte precursor constituted of a lithium element, a sulfurelement, a phosphorus element, a halogen element, and a complexing agentcontaining a compound having at least two tertiary amino groups in themolecule.

Advantageous Effects of Invention

In accordance with the present invention, a solid electrolyte having ahigh ionic conductivity, in which the generation of hydrogen sulfide issuppressed, and an electrolyte precursor by adopting a liquid-phasemethod can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart of explaining one example of preferred modes of aproduction method of the present embodiment.

FIG. 2 is a flow chart of explaining one example of preferred modes of aproduction method of the present embodiment.

FIG. 3 is an X-ray diffraction spectrum of each of an electrolyteprecursor, an amorphous solid electrolyte, and a crystalline solidelectrolyte obtained in Example 1.

FIG. 4 is an X-ray diffraction spectrum of each of raw materials used inExamples.

FIG. 5 is a diagrammatic configuration diagram of a test apparatus usedin an exposure test.

FIG. 6 is a graph showing a change with time of generation amount ofhydrogen sulfide by an exposure test.

FIG. 7 is a graph showing a change with time of cumulative generationamount of hydrogen sulfide by an exposure test.

FIG. 8 is a solid ³¹P-NMR spectrum of an amorphous solid electrolyteobtained in each of Example 8 and Reference Example 2.

FIG. 9 is a solid ³¹P-NMR spectrum of a crystalline solid electrolyteobtained in each of Example 8 and Reference Example 2.

FIG. 10 is an X-ray diffraction spectrum of each of a co-crystal and acrystalline solid electrolyte obtained in Example 16.

FIG. 11 shows cycle characteristics of a positive electrode mixtureshown in Application Examples.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention (hereinafter sometimes referred toas “present embodiment”) are hereunder described. In this specification,numerical values of an upper limit and a lower limit according tonumerical value ranges of “or more”, “or less”, and “XX to YY” are eacha numerical value which can be arbitrarily combined, and numericalvalues of the section of Examples can also be used as numerical valuesof an upper limit and a lower limit, respectively.

[Production Method of Solid Electrolyte]

A production method of a solid electrolyte of the present embodimentincludes mixing a raw material inclusion containing a lithium element, asulfur element, a phosphorus element, and a halogen element with acomplexing agent containing a compound having at least two tertiaryamino groups in the molecule (in this specification, the foregoingcomplexing agent will be sometimes referred to simply as “complexingagent”).

The “solid electrolyte” as referred to in this specification means anelectrolyte of keeping the solid state at 25° C. in a nitrogenatmosphere. The solid electrolyte in the present embodiment is a solidelectrolyte containing a lithium element, a sulfur element, a phosphoruselement, and a halogen element and having an ionic conductivity to becaused owing to the lithium element.

In the “solid electrolyte”, both of a crystalline solid electrolytehaving a crystal structure and an amorphous solid electrolyte, which areobtained by the production method of the present embodiment, areincluded. The crystalline solid electrolyte as referred to in thisspecification is a material that is a solid electrolyte in which peaksderived from the solid electrolyte are observed in an X-ray diffractionpattern in the X-ray diffractometry, and the presence or absence ofpeaks derived from the raw materials of the solid electrolyte does notmatter. That is, the crystalline solid electrolyte contains a crystalstructure derived from the solid electrolyte, in which a part thereofmay be a crystal structure derived from the solid electrolyte, or all ofthem may be a crystal structure derived from the solid electrolyte. Thecrystalline solid electrolyte may be one in which an amorphous solidelectrolyte is contained in a part thereof so long as it has the X-raydiffraction pattern as mentioned above. In consequence, in thecrystalline solid electrolyte, a so-called glass ceramics which isobtained by heating the amorphous solid electrolyte to a crystallizationtemperature or higher is contained.

The amorphous solid electrolyte as referred to in this specification isa halo pattern in which other peak than the peaks derived from thematerials is not substantially observed in an X-ray diffraction patternin the X-ray diffractometry, and it is meant that the presence orabsence of peaks derived from the raw materials of the solid electrolytedoes not matter.

In the production method of a solid electrolyte of the presentembodiment, there are included the following four embodiments dependingupon whether or not a solid electrolyte, such as Li₃PS₄, is used as theraw material, and whether or not a solvent is used. Examples ofpreferred modes of these four embodiments are shown in FIG. 1(Embodiments A and B) and FIG. 2 (Embodiments C and D). That is, in thepresent production method of a solid electrolyte of the presentembodiment, there are preferably included a production method of usingraw materials, such as lithium sulfide and diphosphorus pentasulfide,and a complexing agent (Embodiment B); a production method ofcontaining, as raw materials, Li₃PS₄ that is an electrolyte mainstructure, and the like and using a complexing agent (Embodiment B); aproduction method of adding a solvent to the raw materials, such aslithium sulfide, and the complexing agent in the aforementionedEmbodiment. A (Embodiment C); and a production method of adding asolvent to the raw materials, such as Li₃PS₄, and the complexing agentin the aforementioned Embodiment B (Embodiment D).

The Embodiments A to D are hereunder described in order.

Embodiment

As shown in FIG. 1, the Embodiment A is concerned with a mode in whichin a production method of the present embodiment including mixing a rawmaterial inclusion containing a lithium element, a sulfur element, aphosphorus element, and a halogen element with a complexing agentcontaining a compound having at least two tertiary amino groups in themolecule, lithium sulfide and diphosphorus pentasulfide, and the likeare used as the raw material inclusion. By mixing the raw material,inclusion with the complexing agent, in general, an electrolyteprecursor inclusion that is a suspension is obtained, and by drying it,the electrolyte precursor is obtained. Furthermore, by heating theelectrolyte precursor, the crystalline solid electrolyte is obtained. Inaddition, while not illustrated, it is preferred that the beforeheating, the electrolyte precursor is pulverized, and an electrolyteprecursor pulverized product obtained through pulverization is heated.That is, the present production method preferably includes mixing;pulverization of the electrolyte precursor obtained through mixing; andheating of the electrolyte precursor pulverized product obtained throughpulverization.

While the description is hereunder made beginning from Embodiment A, onedescribed with the wordings “of the present embodiment” is a matterapplicable even in other embodiments.

(Raw Material Inclusion)

The raw material inclusion which is used in the present embodiment isone containing a lithium element, a sulfur element, a phosphoruselement, and a halogen element.

As the raw materials to be contained in the raw material inclusion, forexample, a compound containing at least one of a lithium element, asulfur element, a phosphorus element, and a halogen element can be used.More specifically, representative examples of the foregoing compoundinclude raw materials composed of at least two elements selected fromthe aforementioned four elements, such as lithium sulfide; lithiumhalides, e.g., lithium fluoride, lithium chloride, lithium bromide, andlithium iodide; phosphorus sulfides, e.g., diphosphorus trisulfide(P₂S₃) and diphosphorus pentasulfide (P₂S₅); phosphorus halides, e.g.,various phosphorus fluorides (e.g., PF₃ and P₆), various phosphoruschlorides (e.g., PCl₃, PCl₅, and P₂Cl₄), various phosphorus bromides(e.g., PBr₃ and PBr₅), and various phosphorus iodides (e.g., PI₃ andP₂I₄); and thiophosphoryl halides, e.g., thiophosphoryl fluoride (PSF₃),thiophosphoryl chloride (PSCl₃), thiophosphoryl bromide. (PSBr₃),thiophosphoryl iodide (PSI₃), thiophosphoryl dichlorofluoride (PSCl₂F),and thiophosphoryl dibromofluoride (PSBr₂F), as well as halogen simplesubstances, such as fluorine (F₂), chlorine (Cl₂), bromine (Br₂), andiodine (I₂), with bromine (Br₂) and iodine (I₂) being preferred.

As materials which may be used as the raw material other than thosementioned above, a compound containing not only at least one elementselected from the aforementioned four elements but also other elementthan the foregoing four elements can be used. More specifically,examples thereof include lithium compounds, such as lithium oxide,lithium hydroxide, and lithium carbonate; alkali metal sulfides, such assodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide;metal sulfides, such as silicon sulfide, germanium sulfide, boronsulfide, gallium sulfide, tin sulfide (e.g., SnS and SnS₂), aluminumsulfide, and zinc sulfide; phosphoric acid compounds, such as sodiumphosphate and lithium phosphate; halide compounds of an alkali metalother than lithium, such as sodium halides, e.g., sodium iodide, sodiumfluoride, sodium chloride, and sodium bromide; metal halides, such as analuminum halide, a silicon halide, a germanium halide, an arsenichalide, a selenium halide, a tin halogen, an antimony halide, atellurium halide, and a bismuth halide; and phosphorus oxyhalides, suchas phosphorus oxychloride (POCl₃) and phosphorus oxybromide (POBr₃).

In the Embodiment A, among them, phosphorus sulfides, such as lithiumsulfide, diphosphorus trifluoride (P₂S₃), and diphosphorus pentasulfide(P₂S₅); halogen simple substances, such as fluorine (F₂), chlorine(Cl₂), bromine (Br₂), and iodine (I₂); and lithium halides, such aslithium fluoride, lithium chloride, lithium bromide, and lithium iodideare preferred as the raw material from the viewpoint of more easilyobtaining a solid electrolyte having a high ionic conductivity.Preferred examples of a combination of raw materials include acombination of lithium sulfide, diphosphorus pentasulfide, and a lithiumhalide; and a combination of lithium sulfide, phosphorus pentasulfide,and a halogen simple substance, in which the lithium halide ispreferably lithium bromide or lithium iodide, and the halogen simplesubstance is preferably bromine or iodine.

The lithium sulfide which is used in the Embodiment A is preferably aparticle.

An average particle diameter (D₅₀) of the lithium sulfide particle ispreferably 10 μm or more and 2,000 μm or less, more preferably 30 μm ormore and 1,500 μm or less, and still more preferably 50 μm or more and1,000 μm or less. In this specification, the average particle diameter(D₅₀) is a particle diameter to reach 50% of all the particles insequential cumulation from the smallest particles in drawing theparticle diameter distribution cumulative curve, and the volumedistribution is concerned with an average particle diameter which canbe, for example, measured with a laser diffraction/scattering particlediameter distribution measuring device. In addition, among theabove-exemplified raw materials, the solid raw material is preferablyone having an average particle diameter of the same degree as in theaforementioned lithium sulfide particle, namely one haring an averageparticle diameter falling within the same range as in the aforementionedlithium sulfide particle is preferred.

In the case of using lithium sulfide, diphosphorus pentasulfide, and thelithium halide as the raw materials, from the viewpoint of obtaininghigher chemical stability and a higher ionic conductivity, a proportionof lithium sulfide relative to the total of lithium sulfide anddiphosphorus pentasulfide is preferably 70 to 80 mol %, more preferably72 to 78 mol %, and still more preferably 74 to 76 mol %.

In the case of using lithium sulfide, diphosphorus pentasulfide, alithium halide, and other raw material to be optionally used, thecontent of lithium sulfide and diphosphorus pentasulfide relative to thetotal of the aforementioned raw materials is preferably 60 to 100 mol %,more preferably 65 to 90 mol %, and still more preferably 70 to 80 mol%.

In the case of using a combination of lithium bromide and lithium iodideas the lithium halide, from the viewpoint of enhancing the ionicconductivity, a proportion of lithium bromide relative to the total oflithium bromide and lithium iodide is preferably 1 to 99 mol %, morepreferably 20 to 90 mol %, still more preferably 40 to 80 mol %, andespecially preferably 50 to 70 mol %.

In the case of using not only a halogen simple substance but alsolithium sulfide and &phosphorus pentasulfide as the raw materials, aproportion of the molar number of lithium sulfide excluding lithiumsulfide having the same molar number as the molar number of the halogensimple substance relative to the total molar number of lithium sulfideand diphosphorus pentasulfide excluding lithium sulfide having the samemolar number as the molar number of the halogen simple substance fallspreferably within a range of 60 to 90%, more preferably within a rangeof 65 to 85%, still more preferably within a range of 68 to 82%, yetstill more preferably within a range of 72 to 78%, and even yet stillmore preferably within a range of 73 to 77%. This is because when theforegoing proportion falls within the aforementioned ranges, a higherionic conductivity is obtained. In addition, in the case of usinglithium sulfide, diphosphorus pentasulfide, and a halogen simplesubstance, from the same viewpoint, the content of the halogen simplesubstance relative to the total amount of lithium sulfide, diphosphoruspentasulfide, and the halogen simple substance is preferably 1 to 50 mol%, more preferably 2 to 40 mol %, still more preferably 3 to 25 mol %,and yet still more preferably 3 to 15 mol %,

In the case of using lithium sulfide, diphosphorus pentasulfide, ahalogen simple substance, and a lithium halide, the content (α mol %) ofthe halogen simple substance and the content (β mol %) of the lithiumhalide relative to the total of the aforementioned raw materialspreferably satisfy the following expression (2), more preferably satisfythe following expression (3), still more preferably satisfy thefollowing expression (4), and yet still more preferably satisfy thefollowing expression (5).

2≤(2α+β)≤100   (2)

4≤(2α+β)≤80   (3)

6≤(2α+β)≤50   (4)

6≤(2α+β)≤30   (5)

In the case of using two halogen simple substances, when the molarnumber in the substance of the halogen element of one side is designatedas A1, and the molar number in the substance of the halogen element ofthe other side is designated as A2, an A1/A2 ratio is preferably (1 to99)1(99 to 1), more preferably 10/90 to 90/10, still more preferably20/80 to 80/20, and yet still more preferably 30/70 to 70/30.

In the case where the two halogen simple substances are bromine andiodine, when the molar number of bromine is designated as B1, and themolar number of iodine is designated as B2, a B1/B2 ratio is preferably(1 to 99)1(99 to 1), more preferably 15/85 to 90/10, still morepreferably 20/80 to 80/20, yet still more preferably 30/70 to 75/25, andespecially preferably 35/65 to 75/25.

(Complexing Agent)

In the production method of a solid electrolyte of the presentembodiment, a complexing agent is used, The complexing agent as referredto in this specification is a substance capable of forming a complextogether with the lithium element and means one having such propertiesof acting with the lithium element-containing sulfide and the halide,and the like contained in the aforementioned raw materials, therebypromoting formation of the electrolyte precursor, and in the presentembodiment, one containing a compound having at least two tertiary aminogroups in the molecule (in this specification, the foregoing compoundwill be sometimes referred to simply as “amine compound”) is adopted.

As the complexing agent, any material can be used without beingparticularly restricted so long as it has the aforementioned propertiesand contains a compound having at least two tertiary amino groups in themolecule. In particular, the foregoing compound is one having twotertiary amino group containing a nitrogen element, among elementshaving a high affinity with the lithium element, for example, a heteroelement, such as a nitrogen element, an oxygen element, and a chlorineelement. This is because the amino group containing a nitrogen elementthat is a hetero element may be coordinated (bound) with lithium,especially the tertiary amino group is readily coordinated (bound) withlithium.

Since the complexing agent contains the compound having at least twotertiary amino groups in the molecule, it may be considered that thenitrogen element that is a hetero element in the molecule has a highaffinity with the lithium element, and the complexing agent has suchproperties of binding with the lithium-containing structure which isexistent as a main structure in the solid electrolyte obtained by thepresent production method, such as Li₃PS₄ containing representatively aPS₄ structure, and the lithium-containing raw materials, such as alithium halide, thereby easily forming an aggregate. For that reason,since by mixing the aforementioned raw material inclusion and thecomplexing agent, an aggregate via the lithium-containing structure,such as a PS₄ structure, or the complexing agent, and an aggregate viathe lithium-containing raw material, such as a lithium halide, or thecomplexing agent are evenly existent, whereby an electrolyte precursorin which the halogen element is more likely dispersed and fixed isobtained, as a result, it may be considered that a solid electrolytehaving a high ionic conductivity, in which the generation of hydrogensulfide is suppressed, is obtained.

In view of the fact that the compound having at least two tertiary aminogroups in the molecule, which is contained in the complexing agent to beused in the present embodiment, has at least two hetero elements in themolecule as the tertiary amino groups, the lithium-containing structure,such as Li₃PS₄ containing a PS₄ structure, and the lithium-containingraw material, such as a lithium halide, can be bound with each other viathe at least two hetero elements in the molecule, the halogen element ismore likely dispersed and fixed in the electrolyte precursor. As aresult, a solid electrolyte having a high ionic conductivity, in whichthe generation of hydrogen sulfide is suppressed, is obtained.

The amine compound which is contained in the complexing agent is onehaving at least two tertiary amino groups in the molecule, and in viewof the fact that the complexing agent has such a structure, thelithium-containing structure, such as Li₃PS₄ containing a PS₄ structure,and the lithium containing raw material, such as a lithium halide, canbe bound with each other via at least two nitrogen elements in themolecule, the halogen element is more likely dispersed and fixed in theelectrolyte precursor. As a result, a solid electrolyte having a highionic conductivity is obtained.

Examples of such an amine compound include amine compounds, such asaliphatic amines, alicyclic amines, heterocyclic amines, and aromaticamines, and these amine compounds can be used alone or in combination ofplural kinds thereof. Above all, aliphatic amines are preferred from theviewpoint that the functions of the complexing agent are readilyrevealed.

More specifically, as the aliphatic amine, aliphatic tertiary diamines,such as N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetraethylethylenediamine,N,N,N′,N′-tetramethyldiaminopropane, N,N,N′,N′-tetraethyldiaminopropane,N,N,N′,N′-tetramethyldiaminobutane, N,N,N′,N′-tetramethyldiaminopentane,and N,N,N′,N′-tetramethyldiaminohexane, are representatively preferablyexemplified. Here, in the exemplification in this specification, forexample, when the diaminobutane is concerned, it should be construedthat all of isomers inclusive of not only isomers regarding the positionof the amino group, such as 1,2-bis(dimethylamino)butane,1,3-bis(dimethylamino)butane, and 1,4-bis(dimethylamino)butane, but alsolinear or branched isomers and so on regarding the butane are includedunless otherwise noted.

The carbon number of the aliphatic amine is preferably 2 or more, morepreferably 4 or more, and still more preferably 6 or more, and an upperlimit thereof is preferably 10 or less, more preferably 8 or less, andstill more preferably 7 or less. In addition, the carbon number of thehydrocarbon group of the aliphatic hydrocarbon group in the aliphatictertiary amine is preferably 2 or more, and an upper limit thereof ispreferably 6 or less, more preferably 4 or less, and still morepreferably 3 or less.

As the alicyclic amine, alicyclic tertiary diamines, such asN,N,N′,N′-tetramethyl-cyclohexanediamine andbis(ethylmethylamino)cyclohexane, are representatively preferablyexemplified. As the heterocyclic diamine, heterocyclic tertiary diaminessuch as N,N-dimethylpiperazine and bismethylpiperidylpropane, arerepresentatively preferably exemplified.

The carbon number of each of the alicyclic amine and the heterocyclicamine is preferably 3 or more, and more preferably 4 or more, and anupper limit thereof is preferably 16 or less, and more preferably 14 orless.

As the aromatic amine, aromatic tertiary diamines, such asN,N-dimethylphenylene diamine, N,N,N′,N′-tetramethylphenylenediamineN,N,N′,N′-tetramethyldiaminodiphenylmethane, andN,N,N′,N′-tetramethylnaphthalenediamine, are representatively preferablyexemplified.

The carbon number of the aromatic amine is preferably 6 or more, morepreferably 7 or more, and still more preferably 8 or more, and an upperlimit thereof is preferably 16 or less, more preferably 14 or less, andstill more preferably 12 or less.

The amine compound which is used in the present embodiment may also beone substituted with a substituent, such as an alkyl group, an alkenylgroup, an alkoxy group, a hydroxy group, and a cyano group, or a halogenatom.

While the diamines have been exemplified as specific examples, needlessto say, the amine compound which may be used in the present embodimentis not limited to the diamines so long as it has at least two tertiaryamino groups in the molecule, and for example, polyamines having threeor more amino groups, such asN,N,N′,N″,N″-pentamethyldiethylenetriamine,N,N′-bis[(dimethylamino)ethyl]-N,N′-dimethylethylenediamine, andhexamethylenetetramine, can also be used.

Among those described above, from the viewpoint of obtaining a higherionic conductivity, tertiary diamines having two tertiary amino groupsare more preferred, tertiary diamines having two tertiary amino groupson the both ends are still more preferred, and aliphatic tertiarydiamines having a tertiary amino group on the both ends are yet stillmore preferred. In the aforementioned amine compounds, as the aliphatictertiary diamine having a tertiary amino group on the both ends,tetramethylethylenediamine, tetraethylethylenediamine,tetramethyldiaminopropane, and tetraethyldiaminopropane are preferred,and taking into account easiness of availability and so on,tetramethylethylenediamine and tetramethyldiaminopropane are preferred.

Besides the aforementioned amine compound, other complexing agent may beadded and used. As other complexing agent than the amine compound, forexample, a compound having a group containing a hetero element, such asa halogen element, e.g., an oxygen element and a chlorine element, ishigh in an affinity with the lithium element, and such a compound isexemplified as the other complexing agent than the amine compound. Inaddition, a compound having a group containing, as the hetero element, anitrogen element other than the amino group, for example, a nitro groupand an amide group, provides the same effects. In the present,embodiment, it is preferred that the content of the amine compound inthe complexing agent is high as far as possible. Specifically, theforegoing content is 60% by mass or more, more preferably 80% by mass ormore, still more preferably 90% by mass or more, yet still morepreferably 95% by mass or more, and especially preferably 100% by mass.That is, it is especially preferred that the whole of the complexingagent is the amine compound.

Examples of the other complexing agent include polyamines having threeor more amino groups, such as diethylenetriamine.N,N′,N″-trimethyldiethylenetriamine, triethylenetetramine, andtetraethylenepentamine; diamines, such as aliphatic primary diamines,e.g., ethylenediamine, diaminopropane, and diaminobutane; aliphaticsecondary diamines, e.g., N,N′-dimethylethylenediamine,N,N′-diethylethylenediamine, N,N′-dimethyldiaminopropane, andN,N′-diethyldiaminopropane; alicyclic primary diamines, e.g.,cyclopropanediamine and cyclohexanediamine; alicyclic secondarydiamines, e.g., bisaminoinethylcyclohexane; heterocyclic primarydiamines, e.g.. isophoronediamine; and heterocyclic secondary diamines,e.g., piperazine and dipiperidylpropane; monoamines, such astrimethylamine, triethylamine, ethyldimethyiamine, aliphatic monoaminescorresponding to various diamines, such as the aforementioned aliphaticdiamines, piperidine compounds, such as piperidine, methylpiperidine,and tetramethylpiperidine, pyridine compounds, such as pyridine andpicoline, morpholine compounds, such as morpholine, methvlmorpholine,and thiomorpholine, imidazole compounds, such as imidazole andmethylimidazole, alicyclic monoamines, such as monoamines correspondingto the aforementioned alicyclic diamines, heterocyclic monoamines, suchas monoamines corresponding to the aforementioned heterocyclic diamines,and aromatic monoamines, such as aromatic monoamines corresponding tothe aforementioned aromatic diamines; alcohol-based solvents, such asethanol and butanol; ester-based solvents, such as ethyl acetate andbutyl acetate; aldehyde-based solvents, such as formaldehyde,acetaldehyde, and dimethylforamide; ketone-based solvents, such asacetone and methyl ethyl ketone; ether-based solvents, such as diethylether, diisopropyl ether, dibutyl ether, tetrahydrofuran,dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, andanisole; halogen element-containing aromatic hydrocarbon solvents, suchas trifluoromethylbenzene, nitrobenzene, chlorobenzene, chlorotoluene,and bromobenzene; and solvents containing a carbon atom and a heteroatom, such as acetonitrile, dimethyl sulfoxide, and carbon disulfide. Ofthese, ether-based solvents are preferred; diethyl ether, diisopropylether, dibutyl ether, and tetrahydrofuran are more preferred; anddiethyl ether, diisopropyl ether, and dibutyl ether are still morepreferred.

(Mixing)

As shown in the flow chart of FIG. 1, the raw material inclusion and thecomplexing agent are mixed. In the present embodiment, though a mode ofmixing the raw material inclusion and the complexing agent may be in anyof a solid state and a liquid state, in general, the raw materialinclusion contains a solid, whereas the complexing agent is in a liquidstate, and therefore, in general, mixing is made in a mode in which thesolid raw material inclusion is existent in the liquid complexing agent.

The content of the raw material inclusion is preferably 5 g or more,more preferably 10 g or more, still more preferably 30 g or more, andyet still more preferably 50 g or more relative to the amount of oneliter of the complexing agent, and an upper limit thereof is preferably500 g or less, more preferably 400 g or less, still more preferably 300g or less, and yet still more preferably 250 g of less. When the contentof the raw material inclusion falls within the aforementioned range, theraw material inclusion is readily mixed, the dispersing state of the rawmaterials is enhanced, and the reaction among the raw materials ispromoted, and therefore, the electrolyte precursor and further the solidelectrolyte are readily efficiently obtained.

A method for mixing the raw material inclusion and the complexing agentis not particularly restricted, and the raw materials contained in theraw material inclusion and the complexing agent may be charged in anapparatus capable of mixing the raw material inclusion and thecomplexing agent and mixed. For example, by feeding the complexing agentinto a tank, actuating an impeller, and then gradually adding the rawmaterials, a favorable mixing state of the raw material inclusion isobtained, and dispersibility of the raw materials is enhanced, and thus,such is preferred.

In the case of using a halogen simple substance as the raw material,there is a case where the raw material is not a solid. Specifically,fluorine and chlorine are a gas, and bromine is a liquid under normaltemperature and normal pressure. For example, in the case where the rawmaterial is a liquid, it may be fed into the tank separately from theother raw materials together with the complexing agent, and in the casewhere. the raw material is a gas, the raw material may be fed such thatit is blown into the complexing agent having the raw materials addedthereto.

The production method of a solid electrolyte of the present embodimentis characterized by including mixing the raw material inclusion and thecomplexing agent, and the electrolyte precursor can also be produced bya method not using an instrument to be used for the purpose ofpulverization of solid raw materials, which is generally called apulverizer, such as a medium type pulverizer, e.g., a ball mill and abead mill. According to the production method of a solid electrolyte ofthe present embodiment, by merely mixing the raw material inclusion andthe complexing agent, the raw materials and the complexing agentcontained in the inclusion are mixed, whereby the electrolyte precursorcan be formed. In view of the fact that a mixing time for obtaining theelectrolyte precursor can be shortened, or atomization can be performed,the mixture of the raw material inclusion and the complexing agent maybe pulverized by a pulverizer.

Examples of an apparatus for mixing the raw material inclusion and thecomplexing agent include a mechanical agitation type mixer having animpeller provided in a tank. Examples of the mechanical agitation typemixer include a high-speed agitation type mixer and a double arm typemixer, and a high-speed agitation type mixer is preferably used from theviewpoint of increasing the homogeneity of raw materials in the mixtureof the raw material inclusion and the complexing agent and obtaining ahigher ionic conductivity. In addition, examples of the high-speedagitation type mixer include a vertical axis rotating type mixer and alateral axis rotating type mixer, and mixers of any of these types maybe used.

Examples of a shape of the impeller which is used in the mechanicalagitation type mixer include a blade type, an arm type, a ribbon type, amultistage blade type, a double arm type, a shovel type, a twin-shaftblade type, a flat blade type, and a C type blade type. From theviewpoint of increasing the homogeneity of raw materials in the rawmaterial inclusion and obtaining a higher ionic conductivity, a shoveltype, a flat blade type, a C type blade type, and the like arepreferred.

A temperature condition on the occasion of mixing the raw materialinclusion and the complexing agent is not particularly limited, and forexample, it is −30 to 100° C., preferably −10 to 50° C., and morepreferably around room temperature (23° C.) (for example, (roomtemperature)±about 5° C.). In addition, a mixing time is about 0.1 to150 hours, and from the viewpoint of more uniformly mixing the rawmaterial inclusion and the complexing agent and obtaining a higher ionicconductivity, the mixing time is preferably 1 to 120 hours, morepreferably 4 to 100 hours, and still more preferably 8 to 80 hours.

By mixing the raw material inclusion and the complexing agent, owing toan action of the lithium element, the sulfur element, the phosphoruselement, and the halogen element, all of which are contained in the rawmaterials, with the complexing agent, an electrolyte precursor in whichthese elements are bound directly with each other via and/or not via thecomplexing agent is obtained. That is, in the production method of asolid electrolyte of the present embodiment, the electrolyte precursorobtained through mixing of the raw material inclusion and the complexingagent is constituted of the complexing agent, the lithium element, thesulfur element, the phosphorus element, and the halogen element, and bymixing the raw material inclusion and the complexing agent, a materialcontaining the electrolyte precursor (hereinafter sometimes referred toas “electrolyte precursor inclusion”) is obtained. In the presentembodiment, the resulting electrolyte precursor is not one completelydissolved in the complexing agent that is a liquid, and typically, asuspension containing the electrolyte precursor that is a solid isobtained. In consequence, the present production method of a solidelectrolyte of the present embodiment is corresponding to aheterogeneous system in a so-called liquid-phase method.

(Pulverization)

It is preferred that the production method of a solid electrolyte of thepresent embodiment further includes pulverization of the electrolyteprecursor. By pulverizing the electrolyte precursor, a solid electrolytehaving a small particle diameter is obtained while suppressing thelowering of the ionic conductivity.

The pulverization of the electrolyte precursor in the present embodimentis different from mechanical milling that is a so-called solid-phasemethod and is not one for obtaining an amorphous or crystalline solidelectrolyte owing to a mechanical stress. As mentioned above, theelectrolyte precursor contains the complexing agent, and thelithium-containing structure, such as a PS₄ structure, and the rawmaterials containing lithium, such as a lithium halide, are bound(coordinated) with each other via the complexing agent. Then, it may beconsidered that when the electrolyte precursor is pulverized, fineparticles of the electrolyte precursor are obtained while maintainingthe aforementioned binding (coordination) and dispersing state. Bysubjecting this electrolyte precursor to heat treatment, the componentsbound (coordinated) via the complexing agent are linked with each otherat. the same time of removal of the complexing agent, and the reactionwith the crystalline sulfide solid electrolyte easily takes place. Forthat reason, growth of large particles owing to aggregation of particleswith each other as seen in usual synthesis of a solid electrolyte ishardly generated, and atomization can be readily achieved.

From the viewpoint of performance and production, etc. of anall-solid-battery, it is desired that the particle diameter of the solidelectrolyte is small; however, it is not easy to atomize the solidelectrolyte though pulverization with a bead mill or the like. It ispossible to perform the atomization through wet pulverization using asolvent to some extent; however, the solid electrolyte is liable to bedegraded with the solvent, and aggregation is liable to take placeduring pulverization, resulting in a problem such that an excessive loadis applied for the pulverization. On the other hand, even by performingdry pulverization without using a solvent, it is difficult to achievethe atomization in a sub-micron order. Under such circumstances, thefact that the performance of the all-solid-battery can be enhanced, andthe production efficiency can be enhanced through easy treatment ofperforming pulverization of the electrolyte precursor is a significantadvantage.

Furthermore, since owing to agitation and mixing following thepulverization, an aggregate via the lithium-containing structure, suchas a PS₄ structure, or the complexing agent, and an aggregate via thelithium-containing raw material, such as a lithium halide, or thecomplexing agent are evenly existent, whereby an electrolyte precursorin which the halogen element is more likely dispersed and fixed isobtained, as a result, the effect for obtaining a high ionicconductivity is readily exhibited along with the atomization.

The pulverizer which is used for pulverization of the electrolyteprecursor is not particularly restricted so long as it is able topulverize the particles, and for example, a medium type pulverizer usinga pulverization medium can be used. Among medium type pulverizers,taking into account the fact that the electrolyte precursor is in aliquid state or slurry state mainly accompanied by liquids, such as thecomplexing agent and the solvent, a wet-type pulverizer capable ofcoping with wet pulverization is preferred.

Representative examples of the wet type pulverizer include a wet-typebead mill, a wet-type ball mill, and a wet-type vibration mill, and awet-type bead mill using beads as a pulverization medium is preferredfrom the standpoint that it is able to freely adjust the condition of apulverization operation and is easy to cope with materials having asmaller particle diameter. In addition a dry-type pulverizer, such as adry-type medium type pulverizer, e.g., a dry-type bead mill, a dry-typeball mill, and a dry-type vibration mill, and a dry-type non-mediumpulverizer, e.g., a jet mill, can also be used.

The electrolyte precursor to be pulverized by the pulverizer istypically fed as the electrolyte precursor inclusion which is obtainedby mixing the raw material inclusion and the complexing agent and mainlyfed in a liquid state or slurry state. That is, an object to bepulverized by the pulverizer mainly becomes an electrolyte precursorinclusion liquid or an electrolyte precursor-containing slurry.Accordingly, the pulverizer which is used in the present embodiment ispreferably a flow type pulverizer capable of being optionally subjectedto circulation driving of the electrolyte precursor inclusion liquid orelectrolyte precursor-containing slurry. More specifically, it ispreferred to use a pulverizer of a mode of circulating the electrolyteprecursor inclusion liquid or electrolyte precursor-containing slurrybetween a pulverizer (pulverization mixer) of pulverizing the slurry anda temperature-holding tank (reactor) as disclosed in JP 2010-140893 A.

The size of the bead which is used for the pulverizer may beappropriately selected according to the desired particle diameter andtreatment amount and the like, and for example, it may be about 0.05 mmφor more and 5.0 mmφ or less, and it is preferably 0.1 mmφ or more and3.0 mmφ or less, and more preferably 0.3 mmφ or more and 1.5 mmφ or lessin terms of a diameter of the bead.

As the pulverizer which is used for pulverization of the electrolyteprecursor, a machine capable of pulverizing an object using ultrasonicwaves, for example, a machine called an ultrasonic pulverizer, anultrasonic homogenizer, a probe ultrasonic pulverizer, or the like, canbe used.

In this case, various conditions, such as a frequency of ultrasonicwaves, may be appropriately selected according to the desired averageparticle diameter of the electrolyte precursor, and the like. Thefrequency may be, for example, about 1 kHz or more and 100 kHz or less,and from the viewpoint of more efficiently pulverizing the electrolyteprecursor, it is preferably 3 kHz or more and 50 kHz or less, morepreferably 5 kHz or more and 40 kHz or less, and still more preferably10 kHz or more and 30 kHz or less.

An output which the ultrasonic pulverizer has may be typically about 500to 16,000 W, and it is preferably 600 to 10,000 W. more preferably 750to 5,000 W and still more preferably 900 to 1,500 W.

Although an average particle diameter (D₅₀) of the electrolyte precursorwhich is obtained through pulverization is appropriately determinedaccording to the desire, it is typically 0.01 μm or more and 50 μm orless, preferably 0.03 μm or more and 5 μm or less, more preferably 0.05μm or more and 3 μm or less. By taking such an average particlediameter, it becomes possible to cope with the desire of the solidelectrolyte having a small particle diameter as 1 μm or less in terms ofan average particle diameter.

A time for pulverization is not particularly restricted so long as it isa time such that the electrolyte precursor has the desired averageparticle diameter, and it is typically 0.1 hours or more and 100 hoursor less. From the viewpoint of efficiently regulating the particlediameter to the desired size, the time for pulverization is preferably0.3 hours or more and 72 hours or less, more preferably 0.5 hours ormore and 48 hours or less, and still more preferably 1 hour or more and24 hours or less.

The pulverization may be performed after drying the electrolyteprecursor, such as the electrolyte precursor inclusion or electrolyteprecursor-containing slurry, to form the electrolyte precursor as apowder.

In this case, among the aforementioned pulverizers as exemplified as thepulverizer which may be used in the present production method, any oneof the dry-type pulverizers is preferably used. Besides, the itemsregarding the pulverization, such as a pulverization condition, are thesame as those in the pulverization of the electrolyte precursorinclusion or electrolyte precursor-containing slurry, and the averageparticle diameter of the electrolyte precursor obtained throughpulverization is also the same as that as mentioned above.

(Drying)

The production method of a solid electrolyte of the present embodimentmay include drying of the electrolyte precursor inclusion (typically,suspension). According to this, a powder of the electrolyte precursor isobtained. By performing drying in advance, it becomes possible toefficiently perform heating. The drying and the subsequent heating maybe performed in the same process.

The electrolyte precursor inclusion can be dried at a temperatureaccording to the kind of the remaining complexing agent (complexingagent not incorporated into the electrolyte precursor). For example, thedrying can be performed at a temperature of a boiling point of thecomplexing agent or higher. In addition, the drying can be performedthrough drying under reduced pressure (vacuum drying) by using a vacuumpump or the like at typically 5 to 100° C., preferably 10 to 85° C.,more preferably 15 to 70° C., and still more preferably around roomtemperature (23° C.) (for example, (room temperature)±about 5° C.), tovolatilize the complexing agent.

The drying may be performed by subjecting the electrolyte precursorinclusion to solid-liquid separation by means of filtration with a glassfilter or the like, or decantation, or solid-liquid separation with acentrifuge or the like. In the present embodiment, after performing thesolid-liquid separation, the drying may be performed under theaforementioned temperature condition.

Specifically, for the solid-liquid separation, decantation in which theelectrolyte precursor inclusion is transferred into a container, andafter the electrolyte precursor is precipitated, the complexing agentand solvent as a supernatant are removed, or filtration with a glassfilter having a pore size of, for example, about 10 to 200 μm, andpreferably 20 to 150 μm, is easy.

The electrolyte precursor has such a characteristic feature that it isconstituted of the complexing agent, the lithium element, the sulfurelement, the phosphorus element, and the halogen element, and in theX-ray diffraction pattern in the X-ray diffractometry, peaks differentfrom the peaks derived from the raw materials are observed, and itpreferably contains a co-crystal constituted of the complexing agent,the lithium element, the sulfur element, the phosphorus element, and thehalogen element, When only the raw material inclusion is merely mixed,the peaks derived from the raw materials are merely observed, whereaswhen the raw material inclusion and the complexing agent are mixed,peaks different from the peaks derived from the raw materials areobserved. Thus, the electrolyte precursor (co-crystal) has a structureexplicitly different from the raw materials themselves contained in theraw material inclusion. This matter is specifically confirmed in thesection of Examples. Measurement examples of the X-ray diffractionpatterns of the electrolyte precursor (co-crystal) and the respectiveraw materials, such as lithium sulfide, are shown in FIGS. 3 and 4,respectively. It is noted from the X-ray diffraction patterns that theelectrolyte precursor (co-crystal) has a predetermined crystalstructure. In addition, the diffraction pattern of the electrolyteprecursor does not contain the diffraction patterns of any rawmaterials, such as lithium sulfide, as shown in FIG. 4, and thus, it isnoted that the electrolyte precursor (co-crystal) has a crystalstructure different from the raw materials.

In addition, the electrolyte precursor (co-crystal) has such acharacteristic feature that it has a structure different from thecrystalline solid electrolyte. This matter is also specificallyconfirmed in the section of Examples. The X-ray diffraction pattern ofthe crystalline solid electrolyte is also shown m FIG. 4, and it isnoted that the foregoing diffraction pattern is different from thediffraction pattern of the electrolyte precursor (co-crystal). Theelectrolyte precursor (co-crystal) has the predetermined crystalstructure and is also different from the amorphous solid electrolytehaving a broad pattern as shown in FIG. 4.

The co-crystal is constituted of the complexing agent, the lithiumelement, the sulfur element, the phosphorus element, and the halogenelement, and typically, it may be presumed that a complex structure inwhich the lithium element and the other elements are bound directly witheach other via and/or not via the complexing agent is formed.

Here, the fact that the complexing agent constitutes the co-crystal canbe, for example, confirmed through gas chromatography analysis.Specifically, the complexing agent contained in the co-crystal can bequantitated by dissolving a powder of the electrolyte precursor inmethanol and subjecting the obtained methanol solution to gaschromatography analysis.

Although the content of the complexing agent in the electrolyteprecursor vanes with the molecular weight of the complexing agent, it istypically about 10% by mass or more and 70% by mass or less, and pre era15% by mass or more and 65% by mass or less.

In the production method of a solid electrolyte of the presentembodiment, what the co-crystal containing the halogen element is formedis preferred from the standpoint of enhancing the ionic conductivity. Byusing the complexing agent, the lithium-containing structure, such as aPS₄ structure, and the lithium-containing raw materials, such as alithium halide, are bound (coordinated) with each other via thecomplexing agent, the co-crystal in which the halogen element is morelikely dispersed and fixed is readily obtained, and the ionicconductivity is enhanced.

The matter that the halogen element in the electrolyte precursorconstitutes the co-crystal can be confirmed from the fact that even whenthe solid-liquid separation of the electrolyte precursor inclusion isperformed, the predetermined amount of the halogen element is containedin the electrolyte precursor. This is because the halogen element whichdoes not constitute the co-crystal is easily eluted as compared with thehalogen element constituting the co-crystal and discharged into theliquid of solid-liquid separation. In addition, the foregoing matter canalso be confirmed from the fact that by performing composition analysisthrough ICP analysis (inductively coupled plasma atomic emissionspectrophotometry) of the electrolyte precursor or solid electrolyte, aproportion of the halogen element in the electrolyte precursor or solidelectrolyte is not remarkably lowered as compared with a proportion ofthe halogen element fed from the raw materials.

The amount of the halogen element remaining in the electrolyte precursoris preferably 30% by mass or more, more preferably 35% by mass or more,and still more preferably 40% by mass or more relative to the chargedcomposition. An upper limit of the halogen element remaining in theelectrolyte precursor is 100% by mass.

(Heating)

It is preferred that the production method of a solid electrolyte of thepresent embodiment includes heating of the electrolyte precursor toobtain the amorphous solid electrolyte; and heating of the electrolyteprecursor or amorphous solid electrolyte to obtain the crystalline solidelectrolyte. In view of the fact that heating of the electrolyteprecursor is included, the complexing agent in the electrolyte precursoris removed, and the amorphous solid electrolyte and the crystallinesolid electrolyte each containing the lithium element, the sulfurelement, the phosphorus element, and the halogen element are obtained.In addition, the electrolyte precursor to be heated by the presentbeating may be an electrolyte precursor pulverized product which hasbeen pulverized through the aforementioned pulverization.

Here, the fact that the complexing agent in the electrolyte precursor isremoved is supported by the facts that in addition to the fact that itis evident from the results of the X-ray diffraction pattern, the gaschromatography analysis, and the like that the complexing agentconstitutes the co-crystal of the electrolyte precursor, the solidelectrolyte obtained by removing the complexing agent through heating ofthe electrolyte precursor is identical in the X-ray diffraction patternwith the solid electrolyte obtained by the conventional method withoutusing the complexing agent.

In the production method of the present embodiment, the solidelectrolyte is obtained by heating the electrolyte precursor to removethe complexing agent in the electrolyte precursor, and it is preferredthat. the content of the complexing agent in the solid electrolyte islow as far as possible. However, the complexing agent may be containedto an extent that the performance of the solid electrolyte is notimpaired. The content of the complexing agent in the solid electrolytemay be typically 10% by mass or less, and it is preferably 5% by mass orless, more preferably 3% by mass or less, and still more preferably 1%by mass or less.

In the production method of the present embodiment, in order to obtainthe crystalline solid electrolyte, it may be obtained by heating theelectrolyte precursor, or it may be obtained by heating the electrolyteprecursor to obtain the amorphous solid electrolyte and then heating theamorphous solid electrolyte. That is, in the production method of thepresent embodiment, the amorphous solid electrolyte can also beproduced.

Conventionally, in order to obtain a crystalline solid electrolytehaving a high ionic conductivity, for example, a solid electrolytehaving a thio-LISICON Region II-type crystal structure as mentionedlater, it was required that an amorphous solid electrolyte is preparedthrough mechanical pulverization treatment, such as mechanical milling,or other melt quenching treatment or the like, and then, the amorphoussolid electrolyte is heated. But, it may be said that the productionmethod of the present embodiment is superior to the conventionalproduction method by mechanical milling treatment or the like from thestandpoint that a crystalline solid electrolyte having a thio-LISICONRegion II type crystal structure is obtained even by a method of notperforming mechanical pulverization treatment, other melt quenchingtreatment, or the like.

In the production method of a solid electrolyte of the presentembodiment, whether or not the amorphous solid electrolyte is obtained,whether or not the crystalline solid electrolyte is obtained, whether ornot after obtaining the amorphous solid electrolyte, the crystallinesolid electrolyte is obtained, or whether or not the crystalline solidelectrolyte is obtained directly from the electrolyte precursor isappropriately selected according to the desire, and is able to beadjusted by the heating temperature, the heating time, or the like.

For example, in the case of obtaining the amorphous solid electrolyte,the heating temperature of the electrolyte precursor may be determinedaccording to the structure of the crystalline solid electrolyte which isobtained by heating the amorphous solid electrolyte (or the electrolyteprecursor). Specifically, the heating temperature may be determined bysubjecting the amorphous solid electrolyte (or the electrolyteprecursor) to differential thermal analysis (DTA) with a differentialthermal analysis device (DTA device) under a temperature rise conditionof 10° C/min and adjusting the temperature to a range of preferably 5°C. or lower, more preferably 10° C. or lower, and still more preferably20° C. or lower starting from a peak top temperature of the exothermicpeak detected on the lowermost temperature side. Although a lower limitthereof is not particularly restricted, it may be set to a temperatureof about [(peak top temperature of the exothermic peak detected on thelowermost temperature side)−40° C] or higher. By regulating the heatingtemperature to such a temperature range, the amorphous solid electrolyteis obtained more efficiently and surely. Although the heatingtemperature for obtaining the amorphous solid electrolyte cannot beunequivocally prescribed because it varies with the structure of theresulting crystalline solid electrolyte, in general, it is preferably135° C. or lower, more preferably 130° C. or lower, and still morepreferably 125° C. or lower. Although a lower limit of the heatingtemperature is not particularly limited, it is preferably 90° C. orhigher, more preferably 100° C. or higher, and still more preferably110° C. or higher.

In the case of obtaining the crystalline solid electrolyte by heatingthe amorphous solid electrolyte or directly from the electrolyteprecursor, the heating temperature may be determined according to thestructure of the crystalline solid electrolyte, and it is preferablyhigher than the aforementioned heating temperature for obtaining theamorphous solid electrolyte, Specifically, the heating temperature maybe determined by subjecting the amorphous solid electrolyte (or theelectrolyte precursor) to differential thermal analysis (DTA) with adifferential thermal analysis device (DTA device) under a temperaturerise condition of 10° C/min and adjusting the temperature to a range ofpreferably 5° C. or higher, more preferably 10° C. or higher, and stillmore preferably 20° C. or higher starting from a peak top temperature ofthe exothermic peak detected on the lowermost temperature side. Althoughan upper limit thereof is not particularly restricted, it may be set toa temperature of about [(peak top temperature of the exothermic peakdetected on the lowermost temperature side)+40° C.] or lower. Byregulating the heating temperature to such a temperature range, thecrystalline solid electrolyte is obtained more efficiently and surely.Although the heating temperature for obtaining the crystalline solidelectrolyte cannot be unequivocally prescribed because it varies withthe structure of the resulting crystalline solid electrolyte in general,it is preferably 130° C. or higher, more preferably 135° C. or higher,and still more preferably 140° C. or lower. Although an upper limit ofthe heating temperature is not particularly limited, it is preferably300° C. or lower, more preferably 280° C. or lower, and still morepreferably 250° C. or lower.

Although the heating time is not particularly limited so long as it is atime for which the desired amorphous solid electrolyte or crystallinesolid electrolyte is obtained, for example, it is preferably 1 minute ormore, more preferably 10 minutes or more, still more preferably 30minutes or more, and yet still more preferably 1 hour or more. Inaddition, though an upper limit of the heating temperature is notparticularly restricted, it is preferably 24 hours or less, morepreferably 10 hours or less, still more preferably 5 hours or less, andyet still more preferably 3 hours or less.

It is preferred that the heating is performed in an inert gas atmosphere(for example, a nitrogen atmosphere and an argon atmosphere) or in areduced pressure atmosphere (specially, in vacuo). This is becausedeterioration for example, oxidation) of the crystalline. solidelectrolyte can be prevented from occurring. Although a method forheating is not particularly limited, for example, a method of using ahot plate, a vacuum heating device, an argon gas atmosphere furnace, ora firing furnace can be adopted. In addition, industrially, a lateraldryer or a lateral vibration fluid dryer provided with a heating meansand a feed mechanism, or the like may be selected according to theheating treatment amount.

(Amorphous Solid Electrolyte)

The amorphous solid electrolyte which is obtained by the productionmethod of a solid electrolyte of the present embodiment contains thelithium element, the sulfur element, the phosphorus element, and thehalogen element. As representative examples thereof, there arepreferably exemplified solid electrolytes constituted of lithiumsulfide, phosphorus sulfide, and a lithium halide, such asLi₂S—P₂S₅—LiI, Li₂S—P₂S₅—LiCl, Li₂S—P₂S₅—LiBr, and Li₂S—P₂S₅—LiI—LiBr;and solid electrolytes further containing other element, such as anoxygen element and a silicon element, for example, Li₂S—P₂S₅—Li₂O—LiIand Li₂S—SiS₂S₅—LiI. From the viewpoint of obtaining a higher ionicconductivity, solid electrolytes constituted of lithium sulfide,phosphorus sulfide, and a lithium halide, such as Li₂S—P₂S₅—LiI,Li₂S—P₂S₅—LiCl, Li₂S—P₂S₅—LiBr, and Li₂S—P₂S₅—LiI—LiBr, are preferred.

The kinds of the elements constituting the amorphous solid electrolytecan be confirmed by, for example, an inductivity coupled plasma opticalemission spectrometer (ICP).

In the case where the amorphous solid electrolyte obtained in theproduction method of a solid electrolyte of the present embodiment. isone having at least Li₂S—P₂S₅, from the viewpoint of obtaining a higherionic conductivity, a molar ratio of Li²S, to P₂S₅ is preferably (65 to85)/(15 to 35), more preferably (70 to 80)/20 to 30), and still morepreferably (72 to 78)/22 to 28).

In the case where the amorphous solid electrolyte obtained in theproduction method of a solid electrolyte of the present embodiment isLi₂S—P₂S₅—LiI—LiBr, the total content of lithium sulfide and phosphoruspentasulfide is preferably 60 to 95 mol %, more preferably 65 to 90 mol%, and still more preferably 70 to 85 mol %. In addition, a proportionof lithium bromide relative to the total of lithium bromide and lithiumiodide is preferably 1 to 99 mol %. more preferably 20 to 90 mol %,still more preferably 40 to 80 mol %, and especially preferably 50 to 70mol %.

In the amorphous solid electrolyte obtained in the production method ofa solid electrolyte of the present embodiment, a blending ratio (molarratio) of lithium element to sulfur element to phosphorous element tohalogen atom is preferably (1.0 to 1.8)/(1.0 to 2.0)/0.1 to 0.8)/(0.01to 0.6), more preferably (1.1 to 1.7)/(1.2 to 1.8)/(0.2 to 0.6)/0.05 to0.5), and still more preferably (1.2 to 1.6)/(1.3 to 1.7)/(0.25 to0.5)/(0.08 to 0.4). In addition, in the case of using a combination ofbromine and iodine as the halogen element, a blending ratio (molarratio) of lithium element to sulfur element to phosphorus element tobromine to iodine is preferably (1.0 to 1.8)/(1.0 to 2.0)/(0.1 to0.8)/(0.01 to 3.0)/(0.01 to 0.3), more preferably (1.1 to 1.7)/(1.2 to1.8)/(0.2 to 0.6)/(0.02 to 0.25)/(0.02 to 0.25), still more preferably(1.2 to 1.6)/(1.3 to 1.7)/(0.25 to 0.5)/(0.03 to 0.2)/(0.03 to 0.2), andyet still more preferably (1.35 to 1.45)/(1.4 to 1.7)/(0.3 to0.45)/(0.04 to 0.18)/(0.04 to 0.18). By allowing the blending ratio(molar ratio) of lithium element to sulfur element to phosphorus elementto halogen element to fall within the aforementioned range, it becomeseasy to provide a solid electrolyte having a thio-LISICON Region II-typecrystal structure and having a higher ionic conductivity.

Although the shape of the amorphous solid electrolyte is notparticularly restricted, examples thereof include a granular shape. Theaverage particle diameter (D₅₀) of the granular amorphous solidelectrolyte is, for example, within a range of 0.01 to 500 μm, andpreferably 0.1 to 200 μm.

(Crystalline Solid Electrolyte)

The crystalline solid electrolyte obtained by the production method of asolid electrolyte of the present embodiment may be a so-called glassceramics which is obtained by heating: the amorphous solid electrolyteto a crystallization temperature or higher. Examples of a crystalstructure thereof include an Li₃PS₄ crystal structure, an Li₄P₂S₆crystal structure, an Li₇PS₆ crystal structure, an Li₇P₃S₁₁ crystalstructure, and a crystal structure having peaks at around of 2θ=20.2°and 23.6° (see, for example, JP 2013-16423 A).

In addition, examples thereof include an Li_(4-x)Ge_(1-x)P_(x)S₄-basedthio-LISICON Region H-type crystal structure (see Kanno, et al., Journalof The Electrochemical Society, 148 (7) A512-746 (2001)) and a crystalstructure similar to the Li_(4-x)Ge_(1-x)P_(x)S₄-based thio-LISICONRegion II-type crystal structure (see Solid State Ionics, 177 (2006),2721-2725). Among them, the thio-LISICON Region II-type crystalstructure is preferred as the crystal structure of the crystalline solidelectrolyte obtained by the production method of a solid electrolyte ofthe present embodiment from the standpoint that a higher ionicconductivity is obtained. Here, the “thio-LISICON Region II type crystalstructure” expresses any one of an Li_(4-x)Ge_(1-x)P_(x)S₄-basedthio-LISICON Region II-type crystal structure and a crystal structuresimilar to the Li_(4-x)Ge_(1-x)P_(x)S₄-based thio-LISICON Region II-typecrystal structure. In addition, though the crystalline solid electrolyteobtained by the production method of a solid electrolyte of the presentembodiment may be one having the aforementioned thio-LISICON RegionII-type crystal structure or may be one having the thio-LISICON RegionII-type crystal structure as a main crystal, it is preferably one havingthe thio-LISICON Region II-type crystal structure as a main crystal. Inthis specification, the wording “having as a main crystal” means that aproportion of the crystal structure serving as an object in the crystalstructure is 80% or more, and it is preferably 90% or more, and morepreferably 95% or more. In addition, from the viewpoint of obtaining ahigher ionic conductivity, the crystalline solid electrolyte obtained bythe production method of a solid electrolyte of the present embodimentis preferably one not containing crystalline Li₃PS₄ (β-Li₃PS₄).

In the X-ray diffractometry using a CuKα ray, the Li₃PS₄ crystalstructure gives diffraction peaks, for example, at around 2θ=17.5°,18.3°, 26.1°, 27.3°, and 30.0°; the Li₄P₂S₆ crystal structure givesdiffraction peaks, for example, at around 2θ=16.9°, 27.1°, and 32.5′;the Li₇PS₆ crystal structure gives diffraction peaks, for example, ataround 2θ=15.3°, 25.2°, 29.6°, and 31.0°; the Li₇P₃S₁₁ crystal structuregives diffraction peaks, for example, at. around 2θ=17.8°, 18.5°, 19.7°,21.8°, 23.7°, 25.9°, 29.6°, and 30.0°; the Li_(4-x)Ge_(1-x)P_(x)S₄-basedthio-LISICON Region II-type crystal structure gives diffraction peaks,for example, at around 2θ=20.1°, 23.9° and 29.5°; and the crystalstructure similar to the Li_(4-x)Ge_(1-x)P_(x)S₄-based thio-LISICONRegion II-type crystal structure gives diffraction peaks, for example,at around 20=20.2° and 23.6°. The position of these peaks may varywithin a range of +0.5°,

As mentioned above, in the case when the thio-LISICON Region II-typecrystal structure is obtained in the present embodiment, the foregoingcrystal structure is preferably one not containing crystalline Li₃PS₄(β-Li₃PS₄). FIG. 3 shows an X-ray diffractometry example of thecrystalline solid electrolyte obtained by the production method of thepresent embodiment. In addition, FIG. 4 shows an X-ray diffractometryexample of crystalline Li₃PS₄ (β-Li₃PS₄). As grasped from FIGS. 3 and 4,the solid electrolyte of the present embodiment does not havediffraction peaks at 2θ=17.5° and 26.1°, or even in the case where ithas diffraction patterns, extremely small peaks as compared with thediffraction peaks of the thio-LISICON Region II-type crystal structureare merely detected.

The crystal structure represented by a compositional formulaLi_(7-x)P_(1-y)Si_(y)S₆ or Li_(7+x)P_(1-y)Si_(y)S₆ (x is −0.6 to 0.6,and y is 0.1 to 0.6), which has the aforementioned structure skeleton ofLi₇PS₆ and in which a part of P is substituted with Si, is a cubiccrystal or a rhombic crystal, and is preferably a cubic crystal, and inX-ray diffractometry using a CuKα ray, the crystal structure gives peaksappearing mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°,and 52.0°. The crystal structure represented by the aforementionedcompositional formula Li_(7-x-2y)PS_(6-x-y)Cl_(x)(0.8≤x≤1.7, and 0<y≤(−0.25x+0.5)) is preferably a cubic crystal, and in the X-raydiffractometry using a CuKα ray, the crystal structure gives peaksappearing mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°,and 52.0°. The crystal structure represented by the aforementionedcompositional formula Li_(7-x),P_(6-x)Ha_(x) (Ha represents Cl or Br,and x is preferably 0.2 to 1.8) is preferably a cubic crystal, and inthe X-ray diffractometry using a Cukα ray, the crystal structure givespeaks appearing mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°,47.0°, and 52.0°.

These peak positions may vary within a range of ±0.5°.

Although the shape of the crystalline solid electrolyte is notparticularly restricted, examples thereof include a granular shape, Theaverage particle diameter (D₅₀) of the granular amorphous solidelectrolyte is, for example, within a range of 0.01 to 500 μm, andpreferably 0.1 to 200 μm.

Embodiment B

Next, the Embodiment B is described.

The Embodiment B is concerned with a mode in which in the productionmethod of the present embodiment including mixing a raw materialinclusion containing a lithium element, a sulfur element, a phosphoruselement, and a halogen element with a complexing agent containing acompound having at least two tertiary amino groups in the molecule, rawmaterials containing, as the raw material inclusion, a solidelectrolyte, such as Li₃PS₄, and the like and the complexing agent areused. In the Embodiment A the electrolyte precursor is formed whilesynthesizing the lithium-containing structure, such as Li₃PS₄, existentas a main structure in the solid electrolyte obtained by the productionmethod of the present embodiment, through reaction among the rawmaterials, such as lithium sulfide, and therefore, may be consideredthat a constitution ratio of the aforementioned structure is liable tobecome small.

Then, in the Embodiment B, a solid electrolyte containing theaforementioned structure is previously prepared by means of productionor the like, and this is used as the raw material. According to this, anelectrolyte precursor in which the aforementioned structure and the rawmaterials containing lithium, such the lithium halide, are bound(coordinated) with each other via the complexing agent, and the halogenelement is dispersed and fixed is more likely obtained. As a result, asolid electrolyte having a high ionic conductivity, in which thegeneration of hydrogen sulfide is suppressed, is obtained.

Examples of the raw material containing a lithium element, a sulfurelement, and a phosphorus element, which may be used in the EmbodimentB. include an amorphous electrolyte or crystalline solid electrolytehaving a PS₄ structure as a molecular structure. From the viewpoint ofsuppressing the generation of hydrogen sulfide, a P₂S₇ structure-freeamorphous solid electrolyte or crystalline electrolyte is preferred. Assuch a solid electrolyte, ones produced by a conventionally existingproduction method, such as a mechanical milling method, a slurry method,and a melt, quenching method, can be used, and commercially availableproducts can also be used.

In this case, the solid electrolyte containing a lithium element, asulfur element, and a phosphorus element is preferably an amorphouselectrolyte. The dispersibility of the halogen element in theelectrolyte precursor is enhanced, and the halogen element is easilybound with the lithium element, the sulfur element, and the phosphoruselement in the solid electrolyte, and as a result, a solid electrolytehaving a higher ionic conductivity can be obtained.

FIGS. 6 and 7 each show the evaluation examples of the generation amountof hydrogen sulfide of the crystalline solid electrolyte obtained in theproduction method of the present embodiment. In the crystalline solidelectrolyte according to the present embodiment, the generation ofhydrogen sulfide is not substantially perceived, and it is noted thatthe generation amount of hydrogen sulfide is conspicuously suppressed ascompared with that in the crystalline solid electrolyte by theconventional method along with mechanical milling. As for thesuppression of the generation amount of hydrogen sulfide, the fact thatlithium sulfide is not used as the raw material; the fact that the P₂S₇structure is not contained as the main structure of the electrolyte; thefact that a halogen element with high water absorbency is contained inthe electrolyte structure; and so on may be considered as the reasons.The Embodiment B is able to provide a crystalline solid electrolyte inwhich a higher ionic conductivity is realized by the liquid-phasemethod, and at the same time, the generation amount of hydrogen sulfideis extremely low as not seen traditionally.

The structure of the solid electrolyte can be observed through solid³¹P-NMR spectrometry. Tables 5 and 6 and FIGS. 8 and 9 show solid³¹P-NMR spectrometry examples of an amorphous solid electrolyte and acrystalline solid electrolyte, each of which is obtained by heating theelectrolyte precursor according to the present embodiment, and anamorphous solid electrolyte and a crystalline solid electrolyte, each ofwhich is obtained by the conventional solid-phase method. As graspedfrom Table 5 and FIG. 8, in the amorphous solid electrolyte by theconventional solid-phase method, peaks of a PS₄ ³⁻ structure, a P₂S₇ ⁴⁻structure, and a P₂S₆ ⁴⁻ structure (P_(x)S_(y) ^(a−) structure) assignedto glass appear. In contrast, the glass component contained in theamorphous solid electrolyte according to the present embodiment is onlythe PS₄ ³⁻ structure, but the P₂S₇ ⁴⁻ structure and so on are notobserved.

Furthermore, in the crystalline solid electrolyte (Table 6 and FIG. 9),in the crystalline solid electrolyte according to the conventionalsolid-phase method, a P₂S₆ ⁴⁻ structure (glass) is observed, whereas theglass component contained in the crystalline solid electrolyte accordingto the present embodiment is only the PS₄ ³⁻ structure. In theEmbodiment B, in view of the fact that the amorphous solid electrolytehaving a PS₄ ⁴ structure and the like are used without using Li₂S as theraw material, for example, a crystalline solid electrolyte which doesnot contain a P₂S₇ ⁴⁻ structure (Li₄P₂S₇) and the like which may beproduced during a reaction process between Li₂S and P₂S and in which thegeneration amount of hydrogen sulfide is extremely low is obtained.

In the embodiment B, the content of the amorphous electrolyte having aPS₄ structure or the like is preferably 60 to 100 mol %, more preferably65 to 90 mol %, and still more preferably 70 to 80 mol % relative to thetotal of the raw materials.

In the case of using the amorphous electrolyte having a PS₄ structure orthe like and the halogen simple substance, the content of the halogensimple substance is preferably 1 to 50 mol %, more preferably 2 to 40mol %, still more preferably 3 to 25 mol %, and yet still morepreferably 3 to 15 mol % relative to the amorphous electrolyte having aPS₄ structure or the like

Besides, in the case of using the halogen simple substance and thelithium halide and the case of using the two halogen simple substances,the same as in the Embodiment A is applicable.

In the Embodiment B, in all other cases than the raw materials, forexample, the complexing agent, the mixing, the heating, the drying, theamorphous solid electrolyte, and the crystalline solid electrolyte, andthe like are the same as those described in the Embodiment A.

In the Embodiment B, the matter that what the electrolyte precursor ispulverized is preferred, the pulverizer to be used for pulverization,the matter that after mixing or after drying, the pulverization may beperformed, various conditions regarding pulverization, and so on arealso the same as those in the Embodiment A.

(Embodiments C and D)

As shown in the flow chart of FIG. 2, the Embodiments C and D aredifferent from the Embodiments A and B, respectively from the standpointthat a solvent is added to the raw material inclusion and the complexingagent containing a compound having at least two tertiary amino group inthe molecule. The Embodiments C and D are concerned with a heterogeneousmethod of solid-liquid coexistence, whereas in the Embodiments A and B,the electrolyte precursor that is a solid is formed in the complexingagent that is a liquid. At this time, when the electrolyte precursor iseasily soluble in the complexing agent, there is a case where separationof the components is generated. In the Embodiments C and D, by using asolvent in which the electrolyte precursor is insoluble, elution of thecomponents in the electrolyte precursor can be suppressed.

(Solvent)

In the production method of a solid electrolyte of the Embodiments C andD, it is preferred to add the solvent to the raw material inclusion andthe complexing agent. In view of the fact that the raw materialinclusion and the complexing agent are mixed using the solvent, aneffect to be brought by using the complexing agent, namely an effect inwhich formation of the electrolyte precursor acting with the lithiumelement, the sulfur element, the phosphorus element, and the halogenelement is promoted, an aggregate via the lithium-containing structure,such as a PS₄ structure, or the complexing agent, and an aggregate viathe lithium-containing raw material, such as a lithium halide, or thecomplexing agent are evenly existent, whereby an electrolyte precursorin which the halogen element is more likely dispersed and fixed isobtained, as a result, an effect for obtaining a high ionic conductivityis easily exhibited.

The production method of a solid electrolyte of the present embodimentis a so-called heterogeneous method, and it is preferred that theelectrolyte precursor is not completely dissolved in the complexingagent that is a liquid but deposited. In the Embodiments C and D, byadding the solvent, the solubility of the electrolyte precursor can beadjusted. In particular, the halogen element is liable to be eluted fromthe electrolyte precursor, and therefore, by adding the solvent, theelution of the halogen element is suppressed, whereby the desiredelectrolyte precursor is obtained. As a result, a crystalline solidelectrolyte having a high ionic conductivity, in which the generation ofhydrogen sulfide is suppressed, can be obtained via the electrolyteprecursor in which the components, such as a halogen, are dispersed.

As the solvent having such properties, a solvent having a solubilityparameter of 10 or less is preferably exemplified. In thisspecification, the solubility parameter is described in variousliteratures, for example, “Handbook of Chemistry” (published in 2004,Revised 5th Edition, by Maruzen Publishing Co., Ltd.) and is a value δ((cal/cm³)^(1/2)) calculated according to the following numericalformula (1), which is also called a Hildebrand parameter, SP value.

δ=√{square root over ((ΔH−RT)/V)}  (1)

In the numerical formula (1), ΔH is a molar heating value; R is a gasconstant; T is a temperature; and V is molar volume.

By using the solvent having a solubility parameter of 10 or less, thesolvent has such properties that as compared by the aforementionedcomplexing agent, it relatively hardy dissolves the halogen element, theraw materials containing a halogen element, such as a lithium halide,and further the halogen element-containing component constituting theco-crystal contained in the electrolyte precursor (for example, anaggregate in which lithium halide and the complexing agent are boundwith each other); it is easy to fix the halogen element within theelectrolyte precursor; the halogen element is existent in a favorablestate in the resulting electrolyte precursor and further the solidelectrolyte; and a solid electrolyte having a high ionic conductivity isreadily obtained. That is, it is preferred that the solvent which isused in the present embodiment has such properties that it does notdissolve the electrolyte precursor. From the same viewpoint, thesolubility parameter of the solvent is preferably 9.5 or less, morepreferably 9.0 or less, and still more preferably 8.5 or less.

More specifically, as the solvent which is used in the production methodof a solid electrolyte of the Embodiments C and D, it is possible tobroadly adopt a solvent which has hitherto been used in the productionof a solid electrolyte. Examples thereof include hydrocarbon solvents,such as an aliphatic hydrocarbon solvent, an alicyclic hydrocarbonsolvent, and an aromatic hydrocarbon solvent; and carbon atom-containingsolvents, such as an alcohol-based solvent, an ester-based solvent, analdehyde bayed solvent, a ketone-based solvent, an ether-based solvent,and a solvent containing a carbon atom and a hetero atom. Of these,preferably, a solvent having a solubility parameter falling within theaforementioned range may be appropriately selected and used.

More specifically, examples of the solvent include an aliphatichydrocarbon solvent, such as hexane (7.3), pentane (7.0), 2-ethylhexane,heptane (7.4), octane (7.5), decane, undecane, dodecane, and tridecane;an alicyclic hydrocarbon solvent, such as cyclohexane (8.2) andmethylcyclohexane; an aromatic hydrocarbon solvent, such as benzene,toluene (8.8), xylene (8.8), mesitylene, ethylbenzene (8.8),tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, chlorobenzene(9.5) chlorotoluene (8.8), and bromobenzene; an alcohol-based solvent,such as ethanol (12.7) and butanol (11.4); an ester-based solvent, suchas ethyl acetate (9.1) and butyl acetate (8.5); an aldehyde-basedsolvent, such as formaldehyde, acetaldehyde (10.3), anddimethylformamide (12.1); a ketone-based solvent, such as acetone (9.9)and methyl ethyl ketone; an ether-based solvent, such as diethyl ether(7.4), diisopropyl ether (6.9), dibutyl ether, tetrahydrofuran (9.1),dimethoxyethane (7.3), cyclopentylmethyl ether (8.4), tert-butylmethylether, and anisole; and a solvent containing a carbon atom and a heteroatom, such as acetonitrile (11.9), dimethyl sulfoxide, and carbondisulfide. The numerical values within the parentheses in theaforementioned exemplifications are an SP value.

Of these solvents, an aliphatic hydrocarbon solvent, an alicyclichydrocarbon solvent, an aromatic hydrocarbon solvent, and an ether-basedsolvent are preferred; from the viewpoint of obtaining a higher ionicconductivity more stably, heptane, cyclohexane, toluene, ethylbenzene,diethyl ether, diisopropyl ether, dibutyl ether, dimethoxyethane,cyclopentylmethyl ether, tert-butylmethyl ether, and anisole are morepreferred; diethyl ether, diisopropyl ether, and dibutyl ether are stillmore preferred; diisopropyl ether and dibutyl ether are yet still morepreferred; and dibutyl ether is especially preferred. The solvent whichis used in the present embodiment is preferably the organic solvent asexemplified above and is an organic solvent different from theaforementioned complexing agent. In the present embodiment, thesesolvents may be used alone or in combination of plural kinds thereof.

In the case of using the solvent, the content of the raw materials inthe raw material inclusion may be regulated to one relative to one literof the total amount of the complexing agent and the solvent. Inaddition, the content of the complexing agent relative to the totalamount of the complexing agent and the solvent is preferably 10% by massor more, more preferably 15% by mass or more, and still more preferably20% by mass or more, and an upper limit thereof is preferably 65% bymass or less, more preferably 60% by mass or less, and still morepreferably 55% by mass or less.

As for drying in the Embodiments C and D, the electrolyte precursorinclusion can be dried at a temperature according to the kind of each ofthe remaining complexing agent (complexing agent not incorporated intothe electrolyte precursor) and the solvent. For example, the drying canbe performed at a temperature of a boiling point of the complexing agentor solvent or higher. In addition, the drying can be performed throughdrying under reduced pressure (vacuum drying) by using a vacuum pump orthe like at typically 5 to 100° C., preferably 10 to 5° C., morepreferably 15 to 70° C. and still more preferably around, roomtemperature (23° C.) for example, (room temperature) ±about 5° C.), tovolatilize the complexing agent and the solvent. In addition, in thedrying in the Embodiments C and D, in the case where the solvent remainsin the electrolyte precursor, the solvent, is also removed. However,different from the complexing agent constituting the electrolyteprecursor, the solvent hardly constitutes the electrolyte precursor. Inconsequence, the content of the solvent which may remain in theelectrolyte precursor is typically 3% by mass or less, preferably 2% bymass or less, and more preferably 1% by mass or less.

In the Embodiment C, in all other cases than the solvent, for example,the complexing agent, the mixing, the heating, the drying, the amorphoussolid electrolyte, and the crystalline solid elements, and the like arethe same as those described in the Embodiment A. In addition, in theEmbodiment D, all other cases than the solvent. are the same as thosedescribed in the Embodiment B.

In the Embodiments C and D, the matter that what the electrolyteprecursor is pulverized is preferred, the pulverizer to be used forpulverization, the matter that after mixing or after drying, thepulverization may be performed, various conditions regardingpulverization, and so on are also the same as those in the Embodiment A.

The solid electrolyte which is obtained by the present production methodof a solid electrolyte of the present embodiment has a high ionicconductivity and also has an excellent battery performance, and hardlygenerates hydrogen sulfide, so that it is suitably used for batteries.In the case of adopting a lithium element as the conduction species,such is especially suitable. The solid electrolyte of the presentembodiment may be used for a positive electrode layer, may be used for anegative electrode layer, or may be used for an electrolyte layer. Eachof the layers can be produced by a known method.

(Positive Electrode Mixture and Negative Electrode Mixture)

For example, in the case of using the solid electrolyte for the positiveelectrode layer or the negative electrode layer, by dispersing apositive electrode active material or a negative electrode activematerial in an electrolyte precursor-containing liquid or electrolyteprecursor-containing slurry, each of which is the electrolyte precursorinclusion, mixing them, and drying, the electrolyte precursor isattached onto the active material surface. Furthermore, similar to theaforementioned embodiment, by heating the electrolyte precursor, itbecomes an amorphous solid electrolyte or crystalline solid electrolyte.At this time, by heating together with the active material, the positiveelectrode mixture or negative electrode mixture having the solidelectrolyte attached onto the active material surface is obtained.

As the positive electrode active material, any material can be usedwithout particular restrictions so far as it may promote a batterychemical reaction accompanied by transfer of a lithium ion caused due tothe lithium element to be preferably adopted as an element capable ofrevealing the ionic conductivity in the present embodiment in relationto the negative electrode active material.

Examples of such a positive electrode active material in and from whicha lithium ion can be inserted and released include an oxide-basedpositive electrode active material and a sulfide-based positiveelectrode active material.

Preferably, examples of the oxide based positive electrode activematerial include lithium-containing transition metal complex oxides,such as LMO (lithium manganate), LCO (lithium cobaltate), NMC (lithiumnickel manganese cobaltate), NCA (lithium nickel cobalt aluminate), LNCO(lithium nickel cobaltate), and an olivine type compound (LiMeNPO₄:Me=Fe, Co, Ni, or Mn).

Examples of the sulfide-based positive electrode active material includetitanium sulfide (TiS₂), molybdenum sulfide (MoS₂), iron sulfide (FeSand FeS₂), copper sulfide (CuS), and nickel sulfide (Ni₃S₂).

Besides the aforementioned positive electrode active materials, niobiumselenide (NbSe₃) and so on can also be used.

In the present embodiment, the positive electrode active material can beused alone or in combination of plural kinds thereof.

As the negative electrode active material, any material can be usedwithout particular restrictions so long as it may promote a batterychemical reaction accompanied by transfer of a lithium ion causedpreferably due to the lithium element, such as an element which ispreferably adopted as an element revealing the ionic conductivity in thepresent embodiment, and preferably a metal capable of forming an alloytogether with the lithium element, an oxide thereof, and an alloy of theforegoing metal and the lithium element. As such a negative electrodeactive material in and from which a lithium ion can be inserted andreleased, any material which is known as the negative electrode materialin the battery field can be adopted without restrictions.

Examples of such a negative active material include metallic lithium ora metal capable of forming an alloy together with metallic lithium, suchas metallic lithium, metallic indium, metallic aluminum, metallicsilicon, and metallic tin; an oxide of such a metal; and an alloy ofsuch a metal and metallic lithium.

The electrode active material which is used in the present embodimentmay also be one having a coating layer whose surface is coated.

Examples of the material which forms the coating layer include ionicconductors, such as nitrides or oxides of an element revealing the ionicconductivity in the crystalline sulfide solid electrolyte to be used inthe present embodiment, preferably a lithium element, or complexesthereof. Specifically, examples thereof include lithium nitride (Li₃N);a conductor having a lisicon type crystal structure composed of, as amain structure, Li₄GeO₄, for example, Li_(4-2x)Zn_(x)GO₄; a conductorhaving an Li₃PO₄ type skeleton structure, for example, a thiolisicontype crystal structure, such as Li_(4-x)Ge_(1-x)P_(x)S₄; a conductorhaving a perovskite type crystal structure, such asLa_(2/3-x)Li_(3x)TiO₃; and a conductor having an NASICON type crystalstructure, such as LiTi₂(PO₄)₃.

In addition, examples thereof include lithium titanates, such asLi_(y)Ti_(3-y)O₄ (0<y<3) and Li₄Ti₅O₁₂ (LTO); lithium metalates of ametal belonging to the Group 5 of the periodic table, such as LiNbO₃ andLiTaO₃; and oxide-based conductors, such as Li₂O—B₂O₃—P₂O₅-based,Li₂O—B₂O₃—ZnO-based, and Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂-based materials.

The electrode active material having a coating layer is, for example,obtained by attaching a solution containing various elementsconstituting a material for forming the coating layer onto the surfaceof the electrode active material and burning the electrode activematerial after attachment preferably at 200° C. or higher and 400° C. orlower.

Here, as the solution containing various elements, a solution containingan alkoxide of a metal of every sort, such as lithium ethoxide, titaniumisopropoxide, niobium isopropoxide, and tantalum isopropoxide, may beused. In this case, as the solvent, an alcohol-based solvent, such asethanol and butanol; an aliphatic hydrocarbon solvent, such as hexane,heptane, and octane; an aromatic hydrocarbon solvent, such as benzene,toluene, and xylene; and so on may be used.

The aforementioned attachment may be performed through dipping, spraycoating, or the like.

From the viewpoint of enhancing the production efficiency and thebattery performance, a burning temperature is preferably 200° C. orhigher and 400° C. or lower as mentioned above, and more preferably 250°C. or higher and 390° C. or lower, and a burning time is typically about1 minute to 10 hours, and preferably 10 minutes to 4 hours.

A coverage of the coating layer on a basis of a surface area of theelectrode active material is preferably 90% or more, more preferably 95%or more, and still more preferably 100%, namely it is preferred that theentire surface is coated. In addition, a thickness of the coating layeris preferably 1 nm or more, and more preferably 2 nm or more, and anupper limit thereof is preferably 30 nm or less, and more preferably 25nm or less.

The thickness of the coating layer can be measured throughcross-sectional observation with a transmission electron microscope(TEM), and the coverage can be calculated from the thickness, theelemental analysis value, and the BET surface area of the coating layer.

The aforementioned battery preferably uses a collector in addition tothe positive electrode layer, the electrolyte layer, and the negativeelectrode layer, and the collector can be any known one. For example, alayer formed by coating Au, Pt, Al, Ti, Cu, or the like capable ofreacting with the aforementioned solid electrolyte, with Au or the likecan be used.

[Electrolyte Precursor]

The electrolyte precursor of the present embodiment is constituted of alithium element, a sulfur element, a phosphorus element, a halogenelement, and a complexing agent having at least two tertiary aminogroups in the molecule. The electrolyte precursor of the presentembodiment is the same as the electrolyte precursor described above inthe production method of a solid electrolyte. In addition, the fact thatthe content of the complexing agent in the electrolyte precursor ispreferably 10% by mass or more and 70% by mass or less is also the sameas that in the electrolyte precursor described above in the productionmethod of a solid electrolyte.

EXAMPLES

Next, the present invention is described specifically with reference toExamples, but it should be construed that the present invention is by nomeans restricted by these Examples.

Production Example 1

In a one-liter impeller-provided reaction tank, 15.3 g of lithiumsulfide and 24.7 g of diphosphorus pentasulfide were added in a nitrogenatmosphere. After actuating the impeller, 400 of tetrahydrofuran whichhad been previously cooled to −20° C. was introduced into the container.After naturally raising the temperature to room temperature (23° C.),agitation was continued for 72 hours, the obtained reaction liquidslurry was charged in a glass filter (pore size: 40 to 100 μm) to obtaina solid component, and then, the solid component was dried at. 90° C.,thereby obtaining 38 g of Li₃PS₄ (purity: 90% by mass) as a whitepowder. The obtained powder was subjected to powder X-ray diffractometry(XRD) with an X-ray diffraction (XRD) apparatus (SmartLab apparatus,manufactured Rigaku Corporation). As a result, the foregoing powderexpressed a hallow pattern and confirmed to be amorphous Li₃PS₄.

Production Example 2

The white powder of Li₃PS₄ obtained in Production Example 1 was dried invacuo at 180° C. for 2 hours, thereby obtaining β-Li₃PS₄ (crystalline).

Example 1

Into a stirring bar-containing Schlenk flask (capacity: 100 mL), 1.70 gof the white powder (Li₃PS₄: 1.53 g) obtained in Production Example 1,0.19 g lithium bromide, and 0.28 g of lithium iodide were introduced ina nitrogen atmosphere. After rotating the stirring bar, 20 mL oftetramethylethylenediamine (TMEDA) as a complexing agent was added,agitation was continued for 12 hours, and the obtained electrolyteprecursor inclusion was dried in vacuo (at room temperature: 23° C.) toobtain an electrolyte precursor as a powder. Subsequently, the powder ofthe electrolyte precursor was heated at 120° C. in vacuo for 2 hours,thereby obtaining an amorphous solid electrolyte. Furthermore, theamorphous solid electrolyte was heated at 140° C. vacuo for 2 hours,thereby obtaining a crystalline solid electrolyte (the heatingtemperature for obtaining a crystalline solid electrolyte (140° C. inthis Example) will be sometimes referred to as “crystallizationtemperature”).

A part of each of the obtained powder of the electrolyte precursor andcrystalline solid electrolyte was dissolved in methanol, the obtainedmethanol solution was subjected to gas chromatographic analysis tomeasure the content of tetramethylethylenediamine. The results are shownin Table 2.

The obtained electrolyte precursor, amorphous solid electrolyte, andcrystalline solid electrolyte were subjected to powder X-raydiffractometry (D) with an X-ray diffraction (XRD) apparatus (SmartLabapparatus, manufactured Rigaku Corporation), and X-ray diffractionspectra are shown in FIG. 3. In addition, the obtained amorphous solidelectrolyte was subjected to composition analysis through ICP analysis(inductively coupled plasma atomic emission spectrophotometry). Theresults of the composition analysis are shown in Table 4.

In the X-ray diffraction spectrum of the electrolyte precursor, peaksdifferent from the peaks derived from the used raw materials wereobserved, and an X-ray diffraction pattern different from those of theamorphous solid electrolyte and the crystalline solid electrolyte wasshown. In addition, the raw materials used in this Example 1 (amorphousLi₃PS₄, lithium bromide, and lithium iodide) and the raw materials usedin other Examples (lithium sulfide, diphosphorus pentasulfide, andcrystalline Li₃PS₄) were also subjected to powder X-ray diffractometry(XRD), and X-ray diffraction spectra are shown in FIG. 4. The X-raydiffraction spectrum of the electrolyte precursor showed an X-raydiffraction pattern different from the X-ray diffraction spectra of theraw materials.

In the X-ray diffraction spectrum of the amorphous solid electrolyte,any peak other than the peaks derived from the raw materials wasconfirmed to be absent. In addition, in the X-ray diffraction spectrumof the crystalline solid electrolyte, crystallization peaks weredetected mainly at 2θ=20.2° and 23.6°, and the crystalline solidelectrolyte had a thio-LISICON Region II-type crystal structure. Anionic conductivity of the crystalline solid electrolyte was measured andfound to be 2.90×10⁻³ (S/cm), and the crystalline solid electrolyte wasconfirmed to have a high ionic conductivity.

In this Example, the measurement of the ionic conductivity was performedin the following manner.

From the obtained crystalline solid electrolyte, a circular pellethaving a diameter of 10 mm (cross-sectional area S: 0.785 cm²) and aheight (L) of 0.1 to 0.3 cm was molded to prepare a sample. From the topand the bottom of the sample, electrode terminals were taken, and theion conductivity was measured at 25° C. according to an alternatecurrent impedance method (frequency range: 5 MHz to 0.5 Hz, amplitude:10 mV) to give a Cole-Cole plot. In the vicinity of the right end of thearc observed in the high-frequency side region, a real number part Z′(Ω) at the point at which −Z″(Ω) is the smallest was referred to as abulk resistance R (Ω) of the electrolyte, and according to the followingequation, the ion conductivity σ(S/cm) was calculated.

R=ρ(L/S)

o=1/ρ

Example 2

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example. 1, the complexing agent was changedto one shown in Table 1. With respect to the obtained crystalline solidelectrolyte, the ionic conductivity was measured in the same manner asin Example 1. The results are shown in Table 1.

Example 3

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the raw materials were changed tothose shown in Table 1, and the agitation time was changed to 72 hours.With respect to the obtained crystalline solid electrolyte, the ionicconductivity was measured in the same manner as in Example 1. Theresults are shown in Table 1.

Example 4

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the raw materials and thecomplexing agent were changed to those shown in Table 1, and theagitation time was changed to 72 hours. With respect to the obtainedcrystalline solid electrolyte, the ionic conductivity was measured inthe same manner as in Example 1, The results are shown in Table 1.

Example 5

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the use amount of the complexingagent was changed to 10 mL, 10 mL of heptane was used as the solvent,the agitation time was changed to 24 hours, and the crystallizationtemperature was changed to 160° C. With respect to the obtainedcrystalline solid electrolyte, the ionic conductivity was measured inthe same manner as in Example 1. The results are shown in Table 1.

Example 6

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1. the use amount of the complexingagent was changed to 4.4 mL, 15.6 mL, of diethyl ether was used as thesolvent, the agitation time was changed to 24 hours, and thecrystallization temperature was changed to 180° C. With respect to theobtained crystalline solid electrolyte, the ionic conductivity wasmeasured in the same manner as in Example 1. The results are shown inTable 1.

Example 7

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the use amount of the complexingagent was changed to 4.4 mL, 15.6 mL of diisopropyl ether was used asthe solvent, the agitation time was changed to 24 hours, and thecrystallization temperature was changed to 180° C. With respect to theobtained crystalline solid electrolyte, the ionic conductivity wasmeasured in the same manner as in Example 1. The results are shown inTable 1.

Example 8

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the use amount of the complexingagent was changed to 4.4 mL, 15.6 mL of dibutyl ether was used as thesolvent, the agitation time was changed to 24 hours, and thecrystallization temperature was changed to 180° C. With respect to theobtained crystalline solid electrolyte, the ionic conductivity wasmeasured in the same manner as in Example 1. The results are shown inTable 1.

The content of tetramethylethylenediamine in each of the powderedelectrolyte precursor and crystalline solid electrolyte obtain inExample 8 was measured in the same manner as in Example 1. The resultsare shown in Table 2, In addition, with respect to the amorphous solidelectrolyte obtained in Example 8, the composition analysis wasperformed in the same manner as in Example 1. The results are shown inTable 4.

With respect to the amorphous solid electrolyte and the crystallinesolid electrolyte obtained in Example 8, the solid ³¹P-NMR spectrometrywas performed. The solid ³¹P-NMR spectrometry was performed in thefollowing manner.

-   -   Peak Intensity

About 60 mg of a powdered sample was charged in an NMR test tube, and asolid ³¹P-NMR spectrum was obtained using the following apparatus underthe following condition.

Apparatus: ECZ400R (manufactured by JEOL Ltd.)

Observation nucleus: ³¹P

Observation frequency: 161.944 MHz

Measurement temperature: Room temperature

Pulse sequence: Single pulse (using 90° pulse)

90° pulse width: 3.8 μ

Wait time until the next pulse application after FID measurement.: 300seconds

Magic angle rotation speed: 12 kHz

Accumulation count: 16 times

Measurement range: 250 ppm to 150 ppm

Chemical shift: The chemical shift was obtained using (NH₄)₂HPO₄(chemical shift: 1.33 ppm) as an external reference.

A height from a baseline of each of peaks observed in the obtained solid³¹P-NMR spectrum was designated as the peak intensity.

-   -   Peak Resolution

In the case of performing the peak resolution, the obtained solid³¹P-NMR spectrum is analyzed with a software “FT-NMR” (a softwarerecorded “Data Processing of PT-NMR by Personal Computer” RevisedEdition (Second Edition) (published by Sankyo Publishing Co., Ltd.), todetermine resolved peaks.

According to the aforementioned software, separation peaks, calculatedvalues of NMR signals (observed values), and residual square sums R2 arecalculated from the NMR signals by means of the nonlinear least-squaresmethod. In the case where when a maximum peak height is designated as 1,the residual square sum R2 within an analysis range between the observedvalue and the calculated value becomes 0.007 or less, and the number ofresolved peaks becomes minimum, it is considered that the peakresolution is completed. The results are shown in Tables 5 and 6 andFIGS. 8 and 9.

Example 9

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the complexing agent was changed to5.0 mL of tetramethyldiaminopropane, 15.0 mL of dibutyl ether was usedas the solvent, the agitation time was changed to 24 hours, and thecrystallization temperature was changed to 130° C. With respect to theobtained crystalline solid electrolyte, the ionic conductivity wasmeasured in the same manner as in Example 1. The results are shown inTable 1.

Example 10.

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the raw materials were changed tothose shown in Table 1, the complexing agent was changed to 4.4 ML oftetramethylethylenediamine, 15.6 mL of cyclohexane was used as thesolvent, the agitation was changed to 72 hours, and the crystallizationtemperature was changed to 180° C., With respect to the obtainedcrystalline solid electrolyte, the ionic conductivity was measured inthe same manner as in Example 1. The results are shown in Table 1.

Example 11

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the raw materials were changed tothose shown in Table 1, the complexing agent was changed to 4.4 mL oftetramethylethylenediamine, 15.6 mL of dibutyl ether was used as thesolvent, the agitation time was changed to 72 hours, and thecrystallization temperature was changed to 180° C., With respect to theobtained crystalline solid electrolyte, the ionic conductivity wasmeasured in the same manner as in Example 1, The results are shown inTable 1.

Example 12

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the raw materials were changed tothose shown in Table 1. With respect to the obtained crystalline solidelectrolyte, the ionic conductivity was measured in the same manner asin Example 1. The results are shown in Table 1.

Example 13

An electrolyte precursor, an amorphous solid electrolyte, and acrystalline solid electrolyte were obtained in the same manner as inExample 1, except that in Example 1, the raw materials were changed tothose shown in Table 1. With respect to the obtained crystalline solidelectrolyte, the ionic conductivity was measured in the same manner asin Example 1. The results are shown in Table 1.

Comparative Examples 1 to 8

Electrolyte precursors, amorphous solid electrolytes, and crystallinesolid electrolytes of Comparative Examples 1, 2, 4, and 6 to 8 wereobtained in the same manner as in Example 1, except that in Example 1,the solvent shown in Table 1 was used as the complexing agent. Inaddition, an electrolyte precursor, an amorphous solid electrolyte, anda crystalline solid electrolyte of Comparative Example 3 were obtainedin the same manner as in Example 13, except that in Example 13,dimethoxyethane was used. An electrolyte precursor, an amorphous solidelectrolyte, and a crystalline solid electrolyte of Comparative Example5 were obtained in the same manner as in Example 3, except that inExample 3, tetraethylamine was used.

With respect to the crystalline solid electrolytes obtained inComparative Examples 1 to 8, the ionic, conductivity was measured in thesame manner as in Example 1. The results are shown in Table 1. In thepowder X-ray diffractometry of the crystalline solid electrolytesobtained in Examples 1 to 13, all of the samples had a thio-LISICONRegion II-type crystal structure, and crystalline Li₃PS₄ (β-Li₃PS₄) wasnot observed. On the other hand, in Comparative Examples 1 to 8, all ofthe samples did not have a thio-LISICON Region II-type crystalstructure, and crystalline Li₃PS₄ was observed as the main crystal.

TABLE 1 Complexing agent Raw material and solvent β- Complexing IonicLi₂S P₂S₅ Li₃PS₄ Li₃PS₄ LiBr LiI agent Solvent conductivity Embodiment(g) (g) (g) (g) (g) (g) Kind Kind (mS/cm) Example 1 B — — 1.70 — 0.190.28 TMEDA — 2.9 2 B — — 1.70 — 0.19 0.28 TMPDA — 2.4 3 A 0.59 0.95 — —0.19 0.28 TMEDA — 1.7 4 A 0.59 0.95 — — 0.19 0.28 TMPDA — 1.9 5 D — —1.70 — 0.19 0.28 TMEDA Hep 3.1 6 D — — 1.70 — 0.19 0.28 TMEDA DEE 3.1 7D — — 1.70 — 0.19 0.28 TMEDA DIPE 3.7 8 D — — 1.70 — 0.19 0.28 TMEDA DBE4.3 9 D — — 1.70 — 0.19 0.28 TMPDA DBE 3.7 10 C 0.59 0.95 — — 0.19 0.28TMEDA c-Hex 3.3 11 C 0.59 0.95 — — 0.19 0.28 TMEDA DBE 2.8 12 B — — —1.53 0.19 0.28 TMEDA — 1.1 13 B — — 1.62 — — 0.54 TMEDA — 1.7Comparative 1 B — — 1.70 — 0.19 0.28 DME — 0.4 Example 2 B — — 1.70 —0.19 0.28 THF — 0.8 3 B — — 1.62 — — 0.54 DME — 0.5 4 B — — 1.70 — 0.190.28 DBE — 0.2 5 A 0.59 0.95 — — 0.19 0.28 TEA — 0.2 6 B — — 1.70 — 0.190.28 Pyr — 0.3 7 B — — 1.70 — 0.19 0.28 EDA — 0.1 8 B — — 1.70 — 0.190.28 NBA — 0.1

The raw materials used in the present Examples are as follows.

-   -   Li₂S: Lithium sulfide    -   P₂S₅: Diphosphorus pentasulfide    -   Li₃PS₄: Amorphous Li₃PS₄ obtained in Production Example 1    -   β-Li₃PS₄: Crystalline Li₃ PS₄ obtained in Production Example 2    -   LiBr: Lithium bromide    -   LiI: Lithium iodide

The complexing agents and solvents described in Table 1, which were usedin the present Examples, are as follows.

-   -   TMEDA: Tetramethylethylenediamine        (N,N,N′,N′-tetramethylethylenediamine)    -   TMPDA: Tetramethyldiaminopropane        (N,N,N′,N′-tetramethyl-1,3-diaminopropane)    -   Hep: Heptane    -   DEE: Diethyl ether    -   PIPE: Diisopropyl ether    -   DBE: Dibutyl ether    -   c-Hex: Cyclohexane    -   DME: Dimethoxyethane    -   THF: Tetrahydrofuran    -   TEA: Triethylamine    -   Pyr: Pyridine    -   EDA: Ethylenediamine    -   NBA: n-Butylamine

TABLE 2 Content in electrolyte Content in crystalline precursor solidelectrolyte Complexing Complexing agent Solvent agent Solvent % by mass% by mass % by mass % by mass Example 1 55.0 — 1.2 — 8 53.0 0.5 0.3 Notdetected

From the results of the aforementioned Examples (results shown in Table1), it was conformed that according to the production method of a solidelectrolyte of the present embodiment, by merely mixing the raw materialinclusion and the predetermined complexing agent, a solid electrolytehaving a high ionic conductivity is obtained. It was confirmed that byusing, as the complexing agent, a material containing a compound havingat least two tertiary amino groups (amine compound) in the molecule andusing a combination of the foregoing amine compound and a specifiedsolvent (i.e., an ether-based solvent, an aliphatic hydrocarbon solvent,or an alicyclic hydrocarbon solvent), the ionic conductivity tends to beenhanced. On the other hand, it was confirmed that though ComparativeExamples 1 to 4 and 6 to 8 not using the complexing agent containing acompound having at least two tertiary amino groups in the molecule canbe directly compared with Example 1, and Comparative Example 5 can bedirectly compared with Example 3, in all of the Comparative Examples,the ionic conductivity is remarkably lowered as compared with theExamples. In addition, while according to the production method of thepresent embodiment, an amorphous solid electrolyte can be produced, theproduction method of the present embodiment is preferably used for theproduction of a crystalline solid electrolyte from the viewpoint ofmaximally utilizing its characteristics.

From the results of Table 2, in the electrolyte precursor of Example 1,the complexing agent is contained in an amount of about 55.0% by mass,and besides, the elements caused due to the used raw materials arecontained; however, from the X-ray diffraction spectra of FIGS. 3 and 4,it may be considered that the raw materials themselves are notcontained, but they are contained as a co-crystal constituted, of thecomplexing agent, the lithium element, and the like. In addition, thoughin the electrolyte precursor of Example 8, the solvent (dibutyl ether)is slightly contained, it may be considered that similar to theelectrolyte precursor of Example 1, a co-crystal constituted of thecomplexing agent, the lithium element, and the like is contained.

Example 14

An electrolyte precursor inclusion obtained in the same manner as inExample 1 was charged in a glass filter (pore size: 40 to 100 μm) andsubjected to solid-liquid separation, to obtain an electrolyte precursoras a solid component. The obtained electrolyte precursor was heated invacuo at 120° C. for 2 hours, to obtain an amorphous solid electrolyte.Furthermore., the amorphous solid electrolyte was heated in vacuo at140° C. for 2 hours, to obtain a crystalline solid electrolyte.

The obtained amorphous solid electrolyte was subjected to compositionanalysis through ICP analysis (inductively coupled plasma atomicemission spectrophotometry). The composition analysis results are shownin Table 4. In addition, the obtained crystalline solid electrolyte wassubjected to powder X-ray diffractometry (XRD) in the same manner as inExample 1. As a result, the crystalline solid electrolyte had athio-LISICON Region II-type crystal structure. As a result of themeasurement of ionic conductivity, the foregoing crystalline solidelectrolyte had an ionic conductivity of 2.60×10⁻³ (S/cm) and wasconfirmed to have a high ionic conductivity (see Table 3).

Example 15

An electrolyte precursor inclusion obtained in the same manner as inExample 8 was charged in a glass filter (pore size: 40 to 100 μm) andsubjected to solid-liquid separation, to obtain an electrolyte precursoras a solid component. The obtained, electrolyte precursor was heated invacuo at 120° C. for 2 hours, to obtain an amorphous solid electrolyte.Furthermore, the amorphous solid electrolyte was heated in vacuo at 180°C. for 2 hours, to obtain a crystalline solid electrolyte.

The obtained amorphous solid electrolyte was subjected to compositionanalysis through ICP analysis (inductively coupled plasma atomicemission spectrophotometry). The composition analysis results are shownin Table 4. In addition, the obtained crystalline solid electrolyte wassubjected to powder X-ray diffractometry (XRD) in the same manner as inExample 1. As. a result, the crystalline solid electrolyte had athio-LISICON Region II-type crystal structure, As a result of themeasurement of ionic conductivity, the foregoing crystalline solidelectrolyte had an ionic conductivity of 3.40×10⁻³ (S/cm) and wasconfirmed to have a high ionic conductivity (see Table 3).

Comparative Examples 9 and 10

Electrolyte precursors, amorphous solid electrolytes, and crystallinesolid electrolytes were obtained in the same manner as in Example 14,except that in Example 14, the complexing agent was changed to one shownin Table 3.

The obtained amorphous solid electrolytes were subjected to compositionanalysis through ICP analysis (inductively coupled plasma atomicemission spectrophotometry), The composition analysis results are shownin Table 4. In addition, the obtained crystalline solid electrolyteswere subjected to powder X-ray diffractometry (XRD) in the same manneras in Example 1. As a result, in the crystalline solid electrolytes, athio-LISICON Region II-type crystal structure was not seen, and thecrystalline Li₃PS₄ was a main crystal. The measurement. results of theionic conductivity are shown in Table 3.

With respect to Comparative Examples 1 and 2, the obtained amorphoussolid electrolytes were subjected to composition analysis through ICPanalysis (inductively coupled plasma atomic emission spectrophotometry).The composition analysis results are shown in Table 4.

TABLE 3 Complexing agent Raw material and solvent β- Complexing IonicLi₂S P₂S₅ Li₃PS₄ Li₃PS₄ LiBr LiI agent Solvent conductivity Embodiment(g) (g) (g) (g) (g) (g) Kind Kind (mS/cm) Example 14 B — — 1.70 — 0.190.28 TMEDA — 2.6 15 D — — 1.70 — 0.19 0.28 TMEDA DBE 3.4 Comparative 9 B— — 1.70 — 0.19 0.28 DME — 0.2 Example 10 B — — 1.70 — 0.19 0.28 THF —0.2

TABLE 4 Li P S Br I % by % by % by % by % by mass mass mass mass massExample 1 10.1 13.2 55.2 8.4 13.1 8 10.4 12.9 55.1 8.7 12.8 14 10.8 13.956.6 3.8 14.9 15 10.4 13.2 56.2 7.6 12.7 Comparative 1 10.2 12.8 54.48.8 13.7 Example 2 10.0 12.4 54.3 9.2 14.1 9 11.6 16.9 69.7 0.6 1.2 1011.9 17.3 70.6 0.0 0.2

From Tables 1 and 3, it could not be said that all of the solidelectrolytes of the Comparative Examples not using a materialcontaining, as the complexing agent, the compound having at least twotertiary amino groups in the molecule (amine compound) have a high ionicconductivity,

In the case of not using a complexing agent containing an aminecompound, with respect to the lowering of the ionic conductivity of theobtained solid electrolyte, the composition analysis shown in Table 3reveals that in Comparative Examples 9 and 10 in which the co-crystalwas obtained through solid-liquid separation, the contents of thebromine element and the iodine element are extremely low. It may beassumed that this was caused due to the fact that since the complexingagent containing an amine compound was not used, the halogen elementswere not incorporated into the co-crystal but flew out throughdissolution into the solvent, or the like during the solid-liquidseparation.

In addition, in Comparative Examples 1 and 2 in which the co-crystal wasobtained through drying but not solid-liquid separation, the flowing outof the halogen elements through solid-liquid separation did not takeplace, and thus, the contents of the halogen elements were detectedlargely. But, since the amine compound was not used, the halogenelements were not incorporated into the crystal structure similar toComparative Examples 9 and 10, and even by obtaining the crystallinesolid electrolytes by heating, the halogen elements did not function inthe crystal structure, and thus, it may be assumed that as a result, ahigh ionic conductivity was not obtained.

From the results of Table 3, in comparison between Examples 1 and 14 aswell as between Examples 8 and 15, in which the both are different fromeach other from the standpoint of whether or not the solid-liquidseparation is performed, when the solid-liquid separation was performed,a tendency of lowering in the ionic conductivity was revealed. As shownin Table 4, by performing the solid-liquid separation as in Example 14,it may be conjectured that the halogen elements flew out, resulting ininfluencing the lowering of the ionic conductivity. From the results ofTable 3, with respect to Comparative Examples 9 and 10 not using thecomplexing agent containing an amine compound, it may be conjecturedthat when performing the solid-liquid separation, the flowing out of thehalogen elements became extremely remarkable, and as a result, the ionicconductivity became extremely low.

In addition, from the results of Table 4, with respect to ComparativeExamples 1 and 2, since the flowing out of the halogen elements due tothe solid-liquid separation did not take place, while large quantitiesof the halogen elements are detected, the ionic conductivity of theobtained crystalline solid electrolytes becomes low. From these results,it is noted that in the case of not using a material containing acompound having at least two tertiary amino groups in the molecule(amine compound) as the complexing agent, even when the halogen elementsexist in the crystalline solid electrolyte, a high ionic conductivity isnot obtained. This is caused due to the fact that since the aminecompound was not used as the complexing agent, the halogen elements werehardly incorporated into the crystal structure, and the halogen elementsdid not function in the crystal structure, and thus, it may beconsidered that as a result, a high ionic conductivity was not obtained.

(Exposure Test)

First of all, a testing apparatus to be used for the exposure test(exposure testing apparatus 1) is explained by reference to FIG. 5.

The exposure testing apparatus 1 includes, as main structural elements,a flask 10 for humidifying nitrogen; a static mixer 20 for mixinghumidified nitrogen and non-humidified nitrogen; a dew point meter 30for measuring the moisture of mixed nitrogen M170/DMT152, manufacturedby VAISALA KK); a dual reaction pipe 40 for installing a measuringsample; a dew point meter 50 for measuring the moisture of nitrogendischarged from the dual reaction pipe 40; and a hydrogen sulfidemeasurement analyzer 60 for measuring the concentration of hydrogensulfide contained in discharged nitrogen (Model 3000RS, manufactured byAMI), and these are connected with each other using tubes (notillustrated). A temperature of the flask 10 is set to 10° C. by acooling tank 11.

For the tubes for connecting the respective structural elements, aTeflon (registered trademark) tube having a diameter of 6 mm was used.In this figure, expressions of the tubes are omitted, and insteadthereof, the flows are expressed using arrows.

The procedures of evaluation are as follows.

In a nitrogen glow box set to a dew point of −80° C., about 1.5 g of apowdered sample 41 was weighed and. installed in the inside of thereaction pipe 40 such that it was sandwiched by quartz wools 42,followed by hermetically sealing. The evaluation was performed at roomtemperature (20° C.)

Nitrogen was fed at 0.02 MPa into the apparatus 1 from a nitrogen source(not illustrated). The fed nitrogen passes through a bifurcation pipeBP, and a part thereof is fed into the flask 10 and humidified. Theother is fed as non-humidified nitrogen directly into the static mixer20. The feed amount, of nitrogen into the flask 10 is adjusted by aneedle valve V.

By adjusting a flow rate of each of the non-humidified nitrogen and thehumidified nitrogen by a needle valve-provided flow meter FM, the dewpoint is controlled. Specifically, into the static mixer 20, thenon-humidified nitrogen was fed at a flow rate of 800 mL/min, whereasthe humidified nitrogen was fed at a flow rate of 10 to 30 mL/min. Theboth were mixed, and a dew point of the mixed gas (a mixture of thehumidified nitrogen and the humidified nitrogen) was confirmed with thedew point meter 30.

After adjusting the dew point to a temperature shown in Table 1, athree-way cock 43 was rotated, and the mixed gas was passed through theinside of the reaction pipe 40 for a time shown in Table 1. The amountof hydrogen sulfide contained in the mixed gas having passed through thesample 41 was measured with the hydrogen sulfide measurement analyzer60. The amount of hydrogen sulfide was recorded at 15 minute intervals.In addition, for reference, a dew point of the mixed gas after exposurewas measured with the dew point meter 50.

In order to remove hydrogen sulfide from the nitrogen after measurement,the resulting mixed gas was passed through an alkali trap 70.

With respect to the crystalline solid electrolyte obtained in Example 8,the amorphous Li₃PS₄ obtained in Production Example 1, and thecrystalline solid electrolytes obtained in the following ReferenceExamples 1 and 2, an exposure test was performed according to theaforementioned exposure test method. A graph expressing a change withtime of generation amount of hydrogen sulfide at an exposure time asmeasured at all times is shown in FIG. 6, and a graph expressing achange with time of cumulative generation amount of hydrogen sulfide atan exposure time is shown in FIG. 7.

Reference Example 11

Using “BEAD MILL LMZ015” (manufactured by Ashizawa Finetech Ltd.) as abead mill, 485 g of a zirconia ball having a diameter of 0.5 mm wascharged. A 2.0-liter agitator-provided glass-made reactor was used as areaction tank.

29.66 g of lithium sulfide, 47.83 g of diphosphorus pentasulfide, 14.95g of lithium bromide, 15.36 g of lithium iodide, and 1,200 mL ofdehydrated toluene were charged in the reaction tank, to prepare aslurry. The slurry charged in the reaction tank was circulated at a flowrate of 600 mL/min using a pump within the bead mill apparatus; anoperation of the bead mill was commenced at a circumferential velocityof 10 m/s; the circumferential velocity of the bead mill was changed to12 m/s; hot water (HW) was passed therethrough by means of externalcirculation; and reaction was performed such that an ejectiontemperature of the pump was kept at 70° C. After removing a supernatantof the obtained slurry, the residue was placed on a hot plate and driedat 80° C., thereby obtaining a powdered amorphous solid electrolyte, Theobtained powdered amorphous solid electrolyte was heated at 195° C. for3 hours by using a hot plate installed within a globe box, therebyobtaining a crystalline solid electrolyte, The obtained crystallinesolid electrolyte was subjected to powder X-ray diffractometry (XRD). Asa result, crystallization peaks were detected at 2θ=19.9° and 23.6°.

Reference Example 2

Using “BEAD MILL LMZ015” (manufactured by Ashizawa Finetech Ltd.) as abead mill, 485 g of a zirconia ball having a diameter of 0.5 mm wascharged. A 2.0-liter agitator-provided glass-made reactor was used as areaction tank.

34.77 g of lithium sulfide and 45.87 g of diphosphorus pentasulfide werecharged in the reaction tank, and 1,000 mL of dehydrated toluene wasfurther added to prepare a slurry. The slurry charged in the reactiontank was circulated at a flow rate of 600 mL/min by using a pump withinthe bead mill apparatus; an operation of the bead mill was commenced ata circumferential velocity of 10 m/s; and then, 13.97 g of iodine(manufactured by Wako Pure Chemical Industries, Ltd., Special Grade) and13.19 g of bromine. (manufactured by Wako Pure Chemical Industries,Ltd., Special Grade) dissolved in 200 mL of dehydrated toluene werecharged in the reaction tank.

After completion of charging of iodine and bromine, the circumferentialvelocity of the bead mill was changed to 12 m/s; hot water (HW) waspassed therethrough by means of external circulation; and reaction wasperformed such that an ejection temperature of the pump was kept. at.70° C. After removing a supernatant of the obtained slurry, the residuewas placed on a hot plate and dried at 80° C., thereby obtaining apowdered amorphous solid electrolyte. The obtained powdered amorphoussolid electrolyte was heated at 195° C. for 3 hours by using a hot plateinstalled within a globe box, thereby obtaining a crystalline solidelectrolyte. The obtained crystalline solid electrolyte was subjected topowder X-ray diffractometry (XRD). As a result, crystallization peakswere detected at 2.↓=19.9° and 23.6°. In addition, with respect to theamorphous solid electrolyte and the crystalline solid electrolyteobtained in Reference Example 2, the solid ³¹P-NMR spectrometry wasperformed. The results are shown in Tables 5 and 6 and FIGS. 8 and 9.

TABLE 5 Reference Example 8 Example 2 (after heating (after dryingAssignment at 120° C.) at 80° C.) (peak position) Pmol % Pmol % PS₄ ³⁻(amorphous) 91.2 84.6 (83 to 85 ppm) P₂S₆ ⁴⁻ (amorphous) Not detected11.3 (106 to 108 ppm) P₂S₇ ⁴⁻ (amorphous) Not detected 4.1 (90 to 92ppm) Unclear 8.8 Not detected (92.5 ppm)

TABLE 6 Reference Example 8 Example 2 (after heating (after heatingAssignment at 180° C.) at 195° C.) (peak position) Pmol % Pmol % R-II(1) 32.9 — (92 to 94 ppm) R-II (2) 26 54.3 (88 to 90 ppm) R-II (3) 23.322.7 (76 to 78 ppm) R-III 2.3 1.9 (96 to 98 ppm) Low ionic conductivecrystal — 15.8 (83.5 to 34.5 ppm) PS₄ ³⁻ (amorphous) 10.9 — (83 to 85ppm) P₂S₆ ⁴⁻ (amorphous) — 5.3 (106 to 108 ppm) Unclear 4.6 — (73 to 74ppm)

It was confirmed that in ate amorphous Li₃PS₄ obtained in Example 1, thecrystalline solid electrolyte obtained in Reference Example 1 by theconventional solid-phase method (mechanical milling method), and thecrystalline solid electrode obtained in Reference Example 2 using thehalogen simple substance as the raw material, hydrogen sulfide wasgenerated in an amount of 7 ppm at maximum, and the cumulativegeneration amount after lapsing 120 minutes is more than 1 cc/g, whereasin the solid electrolyte obtained in Example 11 which is concerned withthe production method of the present embodiment, the hydrogen sulfide isnot substantially generated.

With respect to the solid ³¹P-NMR spectra of the amorphous solidelectrolytes of Example 8 and Reference Example 2, the peak resolutionwas performed. As a result, as described in Table 5, peaks assigned tothe PS₄ ³⁻ structure, the P₂S₇ ⁴⁻ structure, and the P₂S₆ ⁴⁻ structure(P_(x)S_(y) ^(a−) structure) and the unclear peak were detected in arange of 60 ppm to 130 ppm. The area of each of the peaks was defined asa1, a2, a3 and a4, respectively, and the sum total of the areas of thesepeaks (=a1+a2+a3 a4) was defined as S_(a). In the phosphorus containedin the amorphous solid electrolyte, the ratio of phosphorus (phosphorusratio, mol %) contained in each of the PS₄ ³⁻ structure, the P₂S₆ ⁴⁻structure, the P₂S₇ ⁴⁻ structure, and the unclear peak (92.5 ppm) wasdetermined according to the following expressions.

Phosphorus ratio of PS₄ ³⁻=100×a1/S_(a)

Phosphorus ratio of P₂S₆ ⁴⁻=100×a2/S_(a)

Phosphorus ratio of P₂S₇ ⁴⁻=100×a3/S_(a)

Phosphorus ratio of unclear peak (92.5 ppm)=100×a4S_(a)

The peak assigned to the glass that is an amorphous solid electrolyte,as obtained from Example 8 was only the PS₄ ³⁻ structure, whereas in theamorphous solid electrolyte obtained from Reference Example 2, inaddition to the PS₄ ³⁻ structure, the P₂S₆ ⁴⁻ structure, the P₂S₇ ⁴⁻structure were also observed.

In the solid ³¹P-NMR spectrometry of the crystalline solid electrolyte,as described in Table 6, the peaks assigned to the thio-LISICON RegionII (R-II) (1) to (3), the thio-LISICON Region III (R-III), the low ionicconductive crystal, the PS₄ ³⁻ structure (glass), the P₂S₆ ⁴⁻ structure(glass), and the unclear peak (73 to 74 ppm) were detected. The area ofeach of the peaks was defined as b1, b2, b3, b4, b5, b6, b7, and b8,respectively, and the sum total of the areas of these peaks(=b1+b2+b3+b4+b5+b6+b7+b8) was defined as S_(b). In the phosphoruscontained in the crystalline solid electrolyte, the ratio of phosphorus(phosphorus ratio, mol %) contained in each of the thio-LISICON RegionII (R-II) (1) to (3), the thio-LISICON Region III (R-III), the low ionicconductive crystal, the PS₄ ³⁻ structure (glass), the P₂ S₆ ⁴⁻ structure(glass), and the unclear peak (73 to 74 ppm) was determined according tothe following expressions. Further, the thio-LISICON Region II (R-II)(1) to (3) are different from each other in the dispersion state of asulfur atom and a halogen atom (Cl, Br) around PS₄ ³⁻ in the crystal ofthe thio-LISICON Region II.

Phosphorus ratio of thio-LISICON Region II (R-II) (1)=100×b1/S_(b)

Phosphorus ratio of thio-LISICON Region II (R-II) (2)=100×b2/S_(b)

Phosphorus ratio of thio-LISICON Region II (R-II) (3)=100×b3/S_(b)

Phosphorus ratio of thio-LISICON Region III (R-III)=100×b4S_(b)

Phosphorus ratio of low ionic conductive crystal=100×b5/S_(b)

Phosphorus ratio of PS₄ ³⁻=100×b6/S_(b)

Phosphorus ratio of P₂S₆ ⁴⁻=100 ×b7S_(b)

Phosphorus ratio of unclear peak (73 to 74 ppm)=100 b8/S_(b)

In the crystalline solid electrolyte of Reference Example 2, the P₂S₆ ⁴⁻structure (amorphous) was observed, whereas in the crystalline solidelectrolyte of Example 8, the P₂S₆ ⁴⁻ structure (amorphous) was notobserved, and the PS₄ ³⁻ structure (amorphous) was observed.

Example 16

Into a one-liter impeller-provided reaction tank, 25.5 g of the whitepowder (Li₃PS₄: 22.9 g) obtained in Production Example 1, 2.8 g oflithium bromide, and 4.3 g of lithium iodide were introduced in anitrogen atmosphere. After rotating the impeller, 544 mL of dibutylether (DBE) as a solvent and 66.5 mL of tetramethylethylenediamine(TMEDA) as a complexing agent were charged, and agitation was continuedfor 24 hours, thereby obtaining an electrolyte precursor inclusion. Apart of the obtained electrolyte precursor inclusion was subjected topulverization treatment while circulating by using acirculation-operable bead mill (“STAR MILL LMZ015 (a trade name)”,manufactured by Ashizawa Finetech Ltd.) for 15 minutes under apredetermined condition (bead diameter: 0.5 mmφ, use amount of bead: 456g (bead filling ratio relative to the pulverization chamber 80%), pumpflow rate: 550 mL/min, circumferential velocity: 8 m/s, mill jackettemperature: 20°0 C.). The pulverization pass number required for thepulverization treatment was 14 passes.

Subsequently, the pulverized electrolyte precursor inclusion containingthe electrolyte precursor inclusion having been subjected topulverization treatment was dried in vacuo at room temperature (23° C.),thereby obtaining a powder of the pulverized electrolyte precursor. Thepowder of the pulverized electrolyte precursor was heated in vacuo at130° C. for 2 hours, to obtain a crystalline solid electrolyte (theheating temperature (130° C. in this Example) for obtaining thecrystalline solid electrolyte is sometimes referred to as“crystallization temperature”).

The obtained electrolyte precursor and crystalline solid electrolytewere subjected to powder X-ray diffractometry (XRD) with an X-raydiffraction (XRD) apparatus (SmartLab apparatus, manufactured RigakuCorporation), and X-ray diffraction spectra are shown in FIG. 10.

In the X-ray diffraction spectrum of the electrolyte precursor, peaksdifferent from the peaks derived from the used raw materials wereobserved, and an X-ray diffraction pattern different from those of theamorphous solid electrolyte and the crystalline solid electrolyte wasshown.

In the X-ray diffraction spectrum of the crystalline solid electrolyte,crystallization peaks were detected mainly at 2θ=20.2° and 23.6°, andthe crystalline solid electrolyte had a thio-LISICON Region II-typecrystal structure. An ionic conductivity of the crystalline solidelectrolyte was measured and found to be 4.1 (mS/cm), and thecrystalline solid electrolyte was confirmed to have a high ionicconductivity. In addition, as a result of measuring the average particlediameter (D₅₀) of the obtained crystalline solid electrolyte, it wasfound to be 1.2 μm. The various conditions, measurement results, and thelike in Example 16 are shown in Table 7.

A part of each of the obtained electrolyte precursor and crystallinesolid electrolyte was dissolved in methanol, the obtained methanolsolution was subjected to gas chromatographic analysis to measure thecontent of tetramethylethylenediamine. The results are shown in Table 8.

Example 17

An electrolyte precursor and a crystalline electrolyte were obtained inthe same manner as in Example 16, except that in Example 16, the time ofthe pulverization treatment was changed from 15 minutes to 30 minutes,and the pulverization pass number was changed from 14 passes to 28passes.

In the X-ray diffraction spectrum of the obtained crystalline solidelectrolyte, crystallization peaks were detected mainly at 2θ=20.2° and23.6°, and the crystalline solid electrolyte had a thio-LISICON RegionII-type crystal structure. An ionic conductivity of the crystallinesolid electrolyte was measured and found to be 3.6 (mS/cm), and thecrystalline solid electrolyte was confirmed to have a high ionicconductivity. In addition, as a result of measuring the average particlediameter (D₅₀) of the obtained crystalline solid electrolyte, it wasfound to be 0.87 μm. The various conditions, measurement results, andthe like in Example 17 are shown in Table 7.

Example 18

An electrolyte precursor and a crystalline electrolyte were obtained inthe same manner as in Example 16, except that in Example 16, the time ofthe pulverization treatment was changed from 15 minutes to 1 hour, andthe pulverization pass number was changed from 14 passes to 55 passes.

In the X-ray diffraction spectrum of the obtained crystalline solidelectrolyte, crystallization peaks were detected mainly at 2θ=20.2° and23.6°, and the crystalline solid electrolyte had a thio-LISICON RegionII-type crystal structure. An ionic conductivity of the crystallinesolid electrolyte was measured and found to be 3.4 (mS/cm), and thecrystalline solid electrolyte was confirmed to have a high ionicconductivity. In addition, as a result of measuring the average particlediameter (D₅₀) of the obtained crystalline solid electrolyte, it wasfound to be 0.19 μm. The various conditions, measurement results, andthe like in Example 18 are shown in Table 7.

TABLE 7 Complexing agent Properties of product and solvent Presence orParticle Raw material Complexing absence of Ionic diameter Li₂S P₂S₅Li₃PS₄ LiBr LiI agent Solvent pulverization conductivity (D₅₀) (g) (g)(g) (g) (g) Kind Kind of precursor (mS/cm) (μm) Example 16 — — 25.5 2.84.3 TMEDA DBE Yes 4.1 1.2  Example 17 — — 25.5 2.8 4.3 TMEDA DBE Yes 3.60.87 Example 18 — — 25.5 2.8 4.3 TMEDA DBE Yes 3.4 0.19

The raw materials, complexing agents, and solvents used in Examples 16to 18 as shown in Table 7 are as follows.

-   -   Li₂S: Lithium sulfide    -   P₂S₅: Diphosphorus pentasulfide    -   Lr₈PS₄: Amorphous Li₃PS₄ obtained in Production Example 1    -   LiBr: Lithium bromide    -   LiI: Lithium iodide        -   TMEDA: Tetramethylethylenediamine            tetramethylethylenediamine)    -   DBE: Dibutyl ether

TABLE 8 Content of complexing Content of agent solvent (% by mass) (% bymass) Electrolyte precursor 53.0 0.3 Crystalline solid 1.1 Less than0.11 electrolyte

From the results of Examples 16 to 18, it was confirmed that the solidelectrolyte having a small particle diameter can be easily produced byadopting the liquid-phase method. In addition, the ionic conductivitywas 3.4 (mS/cm) or more, and the obtained solid electrolytes had a highionic conductivity. In comparison among Examples 16 to 18,by increasingthe time or the pulverization pass number of the pulverizationtreatment, it becomes possible to make the particle diameter smaller,but the ionic conductivity tends to be lowered. In the presentinvention, by adjusting the time or the pulverization pass number of thepulverization treatment, it is possible to obtain desired particlediameter and ionic conductivity.

(Application Example: Example of Positive Electrode Mixture)

To an electrolyte precursor inclusion (inclusion liquid) prepared in thesame manner as in Example 1, an active material was added such that aratio of a crystalline solid electrolyte obtained from this electrolyteprecursor to the active material was 10/90. As a positive electrodeactive material, one in which a coating layer of LTO (Li₄Ti₅O₁₀ wasformed on the surface of LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ (averageparticle diameter (D₅₀): 6.2 μm, BET specific surface area: 0.43 m²/g;hereinafter sometime referred to as “NCA”) was used. DBE was furtheradded, to prepare a precursor slurry of a positive electrode mixture.This slurry was heated in vacuo to achieve drying and crystallization inthe same manner as in Example 1, thereby obtaining a positive electrodemixture.

60 mg of the crystalline solid electrolyte obtained in Example 1 wascharged in a ceramic-made cylinder having a diameter of 10 mm and thenpressure molded to prepare an electrolyte layer.

23.6 mg of the aforementioned positive electrode mixture was charged inan upper part of the electrolyte layer and then pressure-molded toprepare an action electrode. An InLi alloy foil was stuck onto thesurface of the electrolyte layer opposite to the action electrode andthen pressure-molded to prepare a reference electrode also working as acounter electrode. Subsequently, the periphery of the cell was subjectedto screw fastening in four places at intervals of 90°, thereby prepare ahalf-cell having a three-layered structure. As for the InLi alloy, solong as a raw material ratio (Li/In) is 0.8 or less, a reactionpotential of Li deinsertion is kept at a fixed level, and therefore, itcan be used as the reference electrode.

With respect to the obtained half-cell, a cut-off voltage was set 3.6 Vat the charge time and 2.5 V at the discharge time, respectively, acurrent density at the charge and discharge time was fixed at 0.24mAcm⁻², and a cycle characteristic evaluation was performed. As aresult, the charge capacity at the first cycle time was set to 100mAh/g; at the second cycle, the current density was fixed at 1.2 mAcm⁻²,and the charge capacity at the second cycle time became 79 mAh/g; at thethird cycle, the current density was fixed at 2.4 mAcm⁻², and the chargecapacity at the third cycle time became 59 mAh/g; and at the fourthcycle, the current density was fixed at 4.8 mAcm⁻², and the chargecapacity at the fourth cycle time became 25 mAh/g. At the fifth cycle,the current density was fixed at 7.2 mAcm⁻², and the charge capacity atthe fourth cycle time became 8.4 mAh/g. At the sixth cycle, the currentdensity was fixed at 9.6 mAcm⁻², and the charge capacity at the fourthcycle time became 1.2 mAh/g. The foregoing results are shown in FIG. 11in which the abscissa is the C rate, and the ordinate is the chargecapacity.

(Reference Example of Positive Electrode Mixture)

Using a tumbling mill (“Small-size Ball Mill AV Type (model number),manufactured by Asahi Rika Factory, Ltd.), 0.1 g of the crystallinesolid electrolyte obtained in Reference Example 2 and 0.9 g of thepositive electrode active material the same as in the aforementionedExample were mixed at a rotation rate of 600 rpm for 1 hour, to obtainan electrode mixture (positive electrode mixture). Subsequently, ahalf-cell was prepared in the same manner as in the aforementionedExample.

A cut-off voltage was set 3.6 V at the charge time and 2.5 V at thedischarge time, respectively, a current density at the charge anddischarge time was fixed at 0.24 mAcm⁻², and a cycle characteristicevaluation was performed. As a result, the charge capacity at the firstcycle time was set to 45.3 mAh/g; at the second cycle, the currentdensity was fixed at 1.2 mAcm ⁻², and the charge capacity at the secondcycle time became 12 mAh/g; at the third cycle, the current density wasfixed at 2.4 mAcm⁻², and the charge capacity at the third cycle timebecame 5.4 mAh/g; and at the fourth cycle, the current density was fixedat 4.8 mAcm⁻², and the charge capacity at the fourth cycle time became0.4 mAh/g. At the fifth cycle, the current density was fixed at 9.8mAcm⁻², and the charge capacity at the fifth cycle time became 0 mAh/g.The foregoing results are shown in FIG. 11 in which the abscissa is theC rate, and the ordinate is the charge capacity.

INDUSTRIAL APPLICABILITY

In accordance with the production method of a solid electrolyte of thepresent embodiment, a crystalline solid electrolyte which is high in theionic conductivity and excellent in the battery performance and is ableto suppress the generation of hydrogen sulfide can be produced. Thecrystalline solid electrolyte obtained by the production method of thepresent embodiment is suitably used for batteries, especially batteriesto be used for information-related instruments, communicationinstruments, and so on, such as personal computers, video cameras, andmobile phones.

1. A solid electrolyte comprising a thio-LISICON Region II-type crystalstructure, wherein the solid electrolyte does not comprise P₂S₆ ⁴⁻structure.
 2. A solid electrolyte, wherein: (1) a signal of athio-LISICON Region II-type crystal structure is observed in the solid³¹P -NMR spectrometry, and (2) a signal of a P₂S₆ ⁴⁻ structure is notobserved in the solid ³¹P-NMR spectrometry.